Log in Problems on some devices

Hello,
i have a problem with my installation on a pi with Home assistant OS.
For a few weeks everything worked just fine but after some time, without any modification from my side it became impossible to connect to ha via either from the app on my phone or the browser. It says “unable to connect to ha, retrying in 60 seconds”. This keeps on going forever.
But from every other device it is possible to use ha as normal. A few Days ago, completely out of the blue, another device was affected. It just seems to affect some devices but a new installation on the phone does not change anything.
Could someone please help me?
I don’t have any idea why only some devices are affected and the other work as normal.
i have the newest installations installed but I guess that has nothing to do with that.
Thank you in advance,
Julian