OnlyOffice Desktop editors cloud integration: missing files and folders

I recently tried again the OnlyOffice desktop editors (an electron wrapper I guess) with the Nextcloud integration. While it used to work fine a few months ago, it now is failing to show some files and folders in the Nextcloud file browser.

This is a bit odd as it basically just renders it like a webbrowser, but something must have changed in the way Nextcloud18 renders the file browser.

Anyone else has this issue?