So, server is on 18.0.3, client is NextCloud Android (3.11.0). I browse files on the (android) phone. Find one, select “Edit”. The client goes through its moves, “OnlyOffice” animation is displayed, and then “Loading document” appears and stays until hell freezes over (or until I cancel it).
There’s a slight difference in behavior too:
For a file that is downloaded to the mobile client, it actually works. Some of the time. After a few seconds of going from nn%, it reaches 100% and the document is indeed opened for editing.
For a file that is not downloaded, it just loops.
No errors in any of the server log files (nginx, PHP 7.2-fpm).
If I use a web based client, either on the phone or on a desktop computer, OnlyOffice and editing/creating of document works just splendid.