PHP- Header issue

I have no idea how to post a question for support except for here and my purchase of the theme came with 6 months support.

I have a site: denverhousevalues.com and anytime that anyone clicks a link that forwards to the site they get this error:

Warning: Class_PHP-Incomplete_Class has no unserializer in
hmecontenta2pewpnas01_data01463878646htmlwp-contentobject-cache.php on line 894

Warning: cannont modify hearder information – headers already sent by (outpit started athomecontectaspewpnsa01…….

We thought we solved it by adding: add_theme_support(‘avia_no_session_support’);
to the Functions.php file in Appearance > Editor

But now it is happening again and seems to be happening on mobile more than a laptop.

Help please because I have paid advertising out there again and no one can reach the site. Did I chose the wrong Theme?

Thank you!