They had it in today's Q&A and I read it several times in the forum and in the chats that notification system is quite a mess in noble. There seems to be worked on though. Strange: it worked on my fresh install for about a day, then got more and more confused. First the counter of dekko in the launcher didn't stop counting, then teleports notification sounds disappeared, then cinnys. So it seems to be not only an issue of upgraded devices.

@smoore100 You may have to look at installing the minimum Android version requirement before going to UT. You can check with the Volla guys which one is required before upgrading to UT. Cheers.

Today I found that someone has a similar problem with the Volla Phone 22 : https://forums.ubports.com/topic/10983/volla-phone-22-very-laggy-performance/5?_=1756284607730 . Maybe both problems are caused by the same thing.

@TotalSonic : Thanks for the answer!