Deleting old CSS and JS files worked. Thanks for your help Rikard! You can mark this thread as resolved.
Thanks Rikard, the theme is now updated to 5.7.1 and that has fixed most of the weirdness. I’m still missing a few resources though. Here’s the URL structure of the images that aren’t showing up:
https://domain.com/wp-content/uploads/dynamic_avia/avia_posts_css/https:/domain.com/wp-content/uploads/2015/10/image.jpg
As far as I can tell, the missing images are all background images that are in CSS files stored in the /dynamic_avia/avia_posts_css/ folder.
Any idea what’s going on with those?