Nextcloud DAV doesn't sync on FP5

Hello gentle(wo)men,

I have downloaded and installed v1.15 then v1.16 on my FP5 bought directly to Fairphone. It works quite well globally, but I’m unable to sync my actual Nextcloud as a WebDAV account. I have no calendar, no contacts, no tasks. It works well if I use and configure DAVx5 from the store with the native app for the agenda and contacts, I have to add OpenTasks for the tasks.

The server and the phone communicate, because when I configure the DAV account and have to choose a name, my phone suggests the mail address associated with this Nextcloud account, so I suppose credentials are OK. But after that, it’s exactly like my Nextcloud is empty. When I try to sync, the loading bar blinks during half a second, and that’ all. No change, no error message.

Any idea ?