@draharz , Welcome to the community!
First of all I would like to inform you that I can understand your dissatisfaction with a not very stable WIFI very well. On the part of the network we could not register any interruptions.
The following tips could help to improve the WIFI:
- we change your modem from IPv6 to IPv4. Some devices and applications have difficulties with IPv6
- the conversion requires a restart of the modem with possible reset and takes 30 minutes
- you could then try to reposition your modem
- finally, you can download the UPC Connect app on your cell phone and measure your WIFI
- there you can order a Bosster, which amplifies the WIFI signal