Sync/webdav problems after upgrading to nextcloud 20

android client 1.3.13
linux desktop client 1.3.18
nextcloud 20.0.2

operating system linux debian 9 with GNOME

reconstruction of the sync problem:
today, i made an upgrade from nextcloud 19 to nextcloud 20. additionally, i upgraded the joplin desktop client to the latest version (1.3.18). because i was facing sync problems on my android client (which might have lasted for quite some while; i cannot reconstruct this), i did a fresh install of the joplin app on my android device. on the destop client, the syncronization still works fine with unchanged snyc settings. however, on my android client, i can't sync.

sync settings:

sync target: nextcloud

the automatic check of the identical sync settings proof correct in the desktop client, but not in the android client.

any idea what the problem is?

update: meanwhile, the sync setting seem to be correct without having changed them. i suppose it was a problem not related to joplin/nextcloud, but to the firewall.