I don’t think anyone is saying it must be your fault. However, while the symptom is that Tidal playback is sometimes intermittent, it’s clear that the cause of this has not yet been identified.
Because you don’t have a local library, and only use Tidal, it’s difficult to change your source material to see what effect this has on the issue. If you’re not in a position to provide local material, or use Qobuz on a trial basis, as a test, then set up a couple of internet radio stations and use them in My Live Radio to see what impact that has on the issue.
Although you have wired ethernet, the issue could be caused by the network - see here for a recent case of issues caused by a network switch going bad. Could you try different ports on your switches to see if that has any impact on the issue?
Lastly, @nuwriy can turn on diagnostics on your Nucleus - the next time the issue occurs, make a note of the time and tell him. He can then retrieve the logs from the Nucleus and see if they cast a light on what is going on…