Seafile not working anymore, network errror

I have seafile running on a raspberry pi, version 7.05. I used to access the seafile server via Windows, Linux and mobile clients.

Everything worked fine. Yesterday night there was an internet problem (for more than half an hour), which also “irritated” my router, because when I checked the port forwarding rules today, I saw that they were not active anymore in the router. I could activate them, though, without having to add them again.

I am not posting the server logs at this point because everything used to work. I checked the dyndns provider and found out via ping that this works, too. I created the keys for https again, no change. All that works right now is that I can reach the web interface with the internal ip address: https://w.x.y.z

Then the web interface appears and I can log in. The Windows and Linux clients cannot access the seafile libraries anymore, though, via https://myip

If I try to acces the server via the mobile client, using a mobile connection (not wifi), it complains about the certificate and does not let me accept it.

The applet.log of my windows client says:

[03/26/20 17:39:17][network detector] resetting the qt network access manager
[03/26/20 18:00:50]Networkerror
Connection timed out
[03/26/20 18:01:35]ServerStatusService: ignore request for host “MyIP”
[03/26/20 18:01:35][network detector] got a network failure: 99
[03/26/20 18:01:35][api] network error for https://MyIP/api2/auth-token/: Connection timed out

seafile.log keeps saying:

http-tx-mgr.c(783): libcurl failed to GET https://MyIP/seafhttp/protocol-version: Couldn’t connect to server.

On the server side, ccnet.log says:

[03/26/20 18:00:20] …/common/session.c(132): using config file /home/seafile/haiwen/conf/ccnet.conf
[03/26/20 18:00:20] …/common/session.c(455): socket file exists, delete it anyway
[03/26/20 18:00:20] …/common/session.c(484): Listen on /home/seafile/haiwen/ccnet/ccnet.sock for local cl$
[03/26/20 18:00:20] …/common/session.c(290): Update pubinfo file
[03/26/20 18:00:21] …/common/session.c(398): Accepted a local client
[03/26/20 18:00:21] …/common/session.c(398): Accepted a local client
[03/26/20 18:00:21] …/common/session.c(398): Accepted a local client
[03/26/20 18:00:21] …/common/session.c(398): Accepted a local client
[03/26/20 18:00:32] …/common/session.c(398): Accepted a local client
[03/26/20 18:00:32] …/common/peer.c(943): Local peer down

seafile.log --> no error messages
seahub.log --> no errors, either

Any ideas?