Nextcloud ios client app "invalid certificate" bug?

Expected behaviour

iOS App should (a) accept the self-signed certificate, when this is (b) still valid and © is added as an accepted exeption certificate during the first set-up of the app.

Actual behaviour

When accessing the iOS app to see/download documents, every two seconds the message appears: “the certificate for this server is invalid” and “Error: unable to download”. This happens even if you click on “connect anyway” -> “yes” for several times. It seems to be limited to the iOS version, as desktop client and web-access is working fine. It also worked before nextcloud 17 and/or before an app update. Somebody reported this problem also here.

clear cache and reinstall the app and log-in again from scratch does not help.

Steps to reproduce

install ios app, connect to server (login), try to access a file.

iOS version

13.4.1

App version

2.25.9.2

Server version

18.0.4

The discussion is active on github where several users describe the same problem. The problem has also been touched here.