Hey Yigit,

Yes they where our first point of call here is their email from them.

Thank you for contacting WP Engine today! I understand you’re getting some 502 errors and want to figure out what’s going on. I apologize for the issue, but I’m more than happy to help.

I checked your Apache error log and found a timeout error, which is usually our system shutting down a long query and accounts for most 502s:

[Thu Dec 11 11:14:54 2014] [error] [client 86.185.146.22] [WPE Monitoring] Stopwatch php.pod-2608.function.session_start.duration exceeded 200ms. Was: 309ms.\n#0 wpe\\measure\\LoggingStopwatch->logStackTrace(309) called at [/nas/wp/www/common/production/measure.php:198]\n#1 wpe\\measure\\LoggingStopwatch->lap_ended(309) called at [/nas/wp/www/common/production/measure.php:134]\n#2 wpe\\measure\\Stopwatch->lapstart() called at [/nas/wp/www/common/production/measure.php:158]\n#3 wpe\\measure\\Stopwatch->__destruct() called at [/nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php:32]\n#4 session_start() called at [/nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php:32]\n#5 avia_sc_masonry_entries->extra_assets() called at [/nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/shortcode-template.class.php:28]\n#6 aviaShortcodeTemplate->init() called at [/nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/template-builder.class.php:335]\n#7 AviaBuilder->createShortcode() called at [/nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/template-builder.class.php:74]\n#8 AviaBuilder->init()\n#9 call_user_func_array(Array ([0] => AviaBuilder Object ([paths] => Array ([pluginPath] => /nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/,[pluginDir] => avia-template-builder/,[pluginUrl] => http://welldoing.org/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/,%5BassetsURL%5D => http://welldoing.org/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/assets/,%5BassetsPath%5D => /nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/assets/,[imagesURL] => http://welldoing.org/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/images/,%5BconfigPath%5D => /nas/wp/www/cluster-2608/welldoing/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/config/),[shortcode_class] => Array ([avia_sc_blog] => avia_sc_blog Object ([builder] => AviaBuilder Object ( *RECURSION*,[config] => Array ([name] => Blog Posts,[tab] => Content Elements,[icon] => http://welldoing.org/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/images/sc-blog.png,%5Border%5D => 40,[target] => avia-target-insert,[shortcode] => av_blog,[tooltip] => Displays Posts from your Blog,[php_class] => avia_sc_blog,[drag-level] => 3,[drop-level] => -1,[popup_editor] => 1),[elements] => Array ([0] => Array ([name] => Do you want to display blog posts?,[desc] => Do you want to display blog posts or entries from a custom taxonomy?,[id] => blog_type,[type] => select,[std] => posts,[subtype] => Array ([Display blog posts] => posts,[Display entries from a custom taxonomy] => taxonomy)),[1] => Array ([name] => Which categories should be used for the blog?,[desc] => You can select multiple categories here. The Page will then show posts from only those categories.,[id] => categories,[type] => select,[multiple] => 6,[required] => Array ([0] => blog_type,[1] => equals,[2] => posts),[subtype] => cat),[2] => Array ([name] => Which Entries?,[desc] => Select which entries should be displayed by selecting a taxonomy,[id] => link,[fetchTMPL] => 1,[type] => linkpicker,[subtype] => Array ([Display Entries from:] => taxonomy),[multiple] => 6,[required] => Array ([0] => blog_type,[1] => equals,[2] => taxonomy),[std] => category),[3] => Array ([name] => Blog Style,[desc] => Choose the default blog layout here.,[id] => blog_style,[type] => select,[std] => single-big,[no_first] => 1,[subtype] => Array ([Multi Author Blog (displays Gravatar of the article author beside the entry and feature images above)] => multi-big,[Single Author, small preview Pic (no author picture is displayed, feature image is small)] => single-small,[Single Author, big preview Pic (no author picture is displayed, feature image is big)] => single-big,[Grid Layout] => blog-grid)),[4] => Array ([name] => Blog Grid Columns,[desc] => How many columns do you want to display?,[id] => columns,[type] => select,[std] => 3,[required] => Array ([0] => blog_style,[1] => equals,[2] => blog-grid),[subtype] => Array ([1] => 1,[2] => 2,[3] => 3,[4] => 4,[5] => 5)),[5] => Array ([name] => Define Blog Grid layout,[desc] => Do you want to display a read more link?,[id] => contents,[type] => select,[std] => excerpt,[required] => Array ([0] => blog_style,[1] => equals,[2] => blog-grid),[subtype] => Array ([Title and Excerpt] => excerpt,[Title and Excerpt + Read More Link] => excerpt_read_more,[Only Title] => title,[Only Title + Read More Link] => title_read_more,[Only excerpt] => only_excerpt,[Only excerpt + Read More Link] => only_excerpt_read_more,[No Title and no excerpt] => no)),[6] => Array ([name] => Blog Content length,[desc] => Should the full entry be displayed or just a small excerpt?,[id] => content_length,[type] => select,[std] => content,[required] => Array ([0] => blog_style,[1] => not,[2] => blog-grid),[subtype] => Array ([Full Content] => content,[Excerpt] => excerpt,[Excerpt With Read More Link] => excerpt_read_more)),[7] => Array ([name] => Preview Image Size,[desc] => Set the image size of the preview images,[id] => preview_mode,[type] => select,[std] => auto,[subtype] => Array ([Set the preview image size automatically based on column or layout width] => auto,[Choose the preview image size manually (select thumbnail size)] => custom)),[8] => Array ([name] => Select custom preview image size,[desc] => Choose image size for Preview Image,[id] => image_size,[type] => select,[required] => Array ([0] => preview_mode,[1] => equals,[2] => custom),[std] => portfolio,[subtype] => Array ([No Scaling (Original Width X Original Height)] => no scaling,[Thumbnail (150×150)] => thumbnail,[Medium (300×300)] => medium,[Large (1030×1030)] => large,[Widget (36×36)] => widget,[Square (180×180)] => square,[Featured (1500×430)] => featured,[Featured Large (1500×630)] => featured_large,[Extra Large (1500×1500)] => extra_large,[Portfolio (495×400)] => portfolio,[Portfolio Small (260×185)] => portfolio_small,[Gallery (845×684)] => gallery,[Magazine (710×375)] => magazine,[Masonry (705×705)] => masonry,[Entry With Sidebar (845×321)] => entry_with_sidebar,[Entry Without Sidebar (1210×423)] => entry_without_sidebar,[Shop Thumbnail (120×120)] => shop_thumbnail,[Shop Catalog (450×450)] => shop_catalog,[Shop Single (450×999)] => shop_single)),[9] => Array ([name] => Post Number,[desc] => How many items should be displayed per page?,[id] => items,[type] => select,[std] => 3,[subtype] => Array ([All] => -1,[1] => 1,[2] => 2,[3] => 3,[4] => 4,[5] => 5,[6] => 6,[7] => 7,[8] => 8,[9] => 9,[10] => 10,[11] => 11,[12] => 12,[13] => 13,[14] => 14,[15] => 15,[16] => 16,[17] => 17,[18] => 18,[19] => 19,[20] => 20,[21] => 21,[22] => 22,[23] => 23,[24] => 24,[25] => 25,[26] => 26,[27] => 27,[28] => 28,[29] => 29,[30] => 30,[31] => 31,[32] => 32,[33] => 33,[34] => 34,[35] => 35,[36] => 36,[37] => 37,[38] => 38,[39] => 39,[40] => 40,[41] => 41,[42] => 42,[43] => 43,[44] => 44,[45] => 45,[46] => 46,[47] => 47,[48] => 48,[49] => 49,[50] => 50,[51] => 51,[52] => 52,[53] => 53,[54] => 54,[55] => 55,[56] => 56,[57] => 57,[58] => 58,[59] => 59,[60] => 60,[61] => 61,[62] => 62,[63] => 63,[64] => 64,[65] => 65,[66] => 66,[67] => 67,[68] => 68,[69] => 69,[70] => 70,[71] => 71,[72] => 72,[73] => 73,[74] => 74,[75] => 75,[76] => 76,[77] => 77,[78] => 78,[79] => 79,[80] => 80,[81] => 81,[82] => 82,[83] => 83,[84] => 84,[85] => 85,[86] => 86,[87] => 87,[88] => 88,[89] => 89,[90] => 90,[91] => 91,[92] => 92,[93] => 93,[94] => 94,[95] => 95,[96] => 96,[97] => 97,[98] => 98,[99] => 99,[100] => 100)),[10] => Array ([name] => Offset Number,[desc] => The offset determines where the query begins pulling posts. Useful if you want to remove a certain number of posts because you already query them with another blog or magazine element.,[
Looks like it’s coming from the theme. I would provide this error to the theme developer and ask how it can be optimized. I also took a look at all of the queries being run by your site via an internal tool:

http://cl.ly/image/1e2b452Y0I39

Since most of the queries being run are coming from the theme, most of the drag and errors you may be experiencing will be related to the theme.