Nextcloud - Onlyoffice problem to open new documents

Nextcloud Hub 8 (29.0.3) (linux native install). Migrated successfully from owncloud (our old installation)
Onlyoffice Enterprise, latest version (on different server on the same internal network)
Nextcloud onlyoffice connector 9.4.0

Nextcloud-onlyoffice connection works.
I can successfully edit documents on onlyoffice, that were previously existed on the users accounts (the ones that came from the old installation of owncloud)

However, I cannot edit in onlyoffice ANY NEW document I create through the nextcloud, or upload from my PC to nextcloud. Those documents have a different icon from the ones migrated and already existed inside users account previously.

The error message when onlyoffice tries to open is:
“Download failed. Press OK to return to document list”

I would appreciate some help here please, if one had ever the same problem.

Any ideas what might cause the issue please?