Failed to connect to Collabora Online - URL port ignored by config

Just upgraded my Nextcloud to v20.08 and CollaboraOnline to v3.7.17
I use a self-hosted CODE server up and running, port 9980 is public exposed and not firewalled.
No docker for NC nor for CODE. No reverse proxy for CODE.
I get “Ok” visiting the page that worked so well until NC upgrade.
Certificates are ok, loowsd report no errors starting up.
The settings page of the CollaboraOnline app says:
“Could not establish connection to the Collabora Online server” with the URL “
I sniffed the network traffic incoming to the CODE server when I try to save the CollaboraOnline URL, and I noticed the connection is ALWAYS attempted on port 443, no matters if I specify “” in the URL
So I suppose the port specification is totally IGNORED
I read something about such issue rising up with version 3.6.0 of CollaboraOnline app, but I can’t find the post anymore.
Can anyone point me in the right direction to solve the issue?
Many thanks!

No one has any clue?