Hello,
I have exactly same issue !
we are using latest version of Joomla Release 3.10.8 and JCE 2.9.22 PRO - the issue happens on various pages with different templates.
When we are creating or updating a Joomla article in frontend, there is tab picture and links.
When we try to insert a picture there is error: Server-IP-Adress index.php does not exist
Interestingly the underlying URL (example) is:
https://index.php/?option=com_jce&task= ... ro&folder=
but I would expect to see our domain name and not just index.php which obviously does not exist.
In the backend there is no issue accessing the folder of the pictures.