Can't reach Nextcloud

Hello Community,
I have a rather weird problem. My Nextcloud is up and running since quite a while. Never really had a problem with it. I have a Domain purchased on Ionos that i connected to my UDM Pro with an Dynamic DNS. Works great since a while. I regularly update my Nextcloud installation. I did not do that the past two weeks. Nextcloud is installed in an Container on Proxmox. Every other thing running on Proxmox like Home Assistant is running fine.
Yesterday evening everything worked fine. When i woke up today Nextcloud was not reachable. When I try reaching it from the web with either my Domain or my public IP or my local IP in my Network I get a Unable to connect error.
I tried restarting my UDM Pro, Proxmox and Nextcloud. I obviously still have access to the Nextcloud console. That seems to work great.
I have no glue why I have this error nad therfore don’t know which error logs could be helpful. If somebody has an Idee just let me know. I can provide the additional information.
Thanks for help