Maryna,
I wish I could.... I'm using a 3rd party SaaS called Bugsnag that logs JavaScript errors that I don't trap myself. I check the logs from time to time, and after my latest upgrade of Oct 1st, I noticed these specific bugs started to emerge, bugs that I had never seen before.
As far as I can judge, they indicate failure to load resources, so the code that references these resources (Appery functions) fails and the error fires.
I think that some of Appery's core JS code is prone to such errors because it runs as soon as it loads, assuming that other resources have loaded. For example, appery.js is an IIFE (Immediately invoked Function Expression) taking jQuery as argument, assuming that jQuery is loaded! There's no guarantee that resources load in any particular order.
There are no edited source files in my project (except my own JS of course...)
Benny