Can you take time to unpublish module and plugin not joomla core, one by one, and test when it works ?

Begin with all extension with jQuery or Mootools.

I also suggested I check the javascript conflicts,
it may be that the user is not so advanced that it can be adjusted independently.
problems of conflict there are often many components.

google search:joomla jquery mootools resolve conflicts,

a lot of documentation is available