Are you using the official mobile apps?
I'm not using official apps, but those same apps work perfectly in version 4.8
I don't think there were any changes on the server that would affect it.
I did a test, downloaded clean 4.8 and 4.11. At 4.8 it worked perfectly and at 4.11 it didn't, I'm intrigued by that. I was needing to update, but give this error.
Does it work with the official apps?
I tested it here with traccar manager and it worked. Too weird
I noticed that in versions 4.10 and 4.11 push notifications are not working because traccar is not creating the notificationTokens attribute. Is anyone experiencing the same problem or has it gone and solved it?