It seems that I have found the causes. First of all it turned out to be necessary to reset the modem. After that, all my carefully set static IP addresses were gone. But there were still a few in the wrong range left. So they were fixed in the device in question and not in the modem.
The second problem was in my Android tablet. That automatically connected to a Wi-Fi point further away. This happened during the access point reboot on my set. When the much better Wi-Fi point was active, it hangs on the weaker Wi-Fi point.
The modem has therefore been reset and provided with the correct static IP addresses. I replaced the Tablet with an Android 11 tablet that will only be used for the set. TuneBrowser is now Ramdecode off and 256 kB cache.
I haven’t had any problems since these changes. I hope it stays this way.
Thanks again for great service.