Bitrix. Standard Ajax not working in AJAX_MODE => Y components?

Question

1C-Bitrix

I got a site made on Bitrix for improvement, in some places the code is written poorly, the site structure is also replete with unnecessary files, folders, scripts, etc.
In general, I wanted to transfer some components to Ajax mode. But I ran into an incomprehensible error Uncaught SyntaxError: Unexpected token < it points to 1 line, and it appears exactly after the request is executed, I don’t quite understand what can cause it? What could be causing such a mess?
For the first time I see this. Attached a screenshot.