Martyn: Thank you for your help! At the very least I would expect PicoScope to issue a warming telling me what the problem is, and, as an added bonus, what I need to do to make the spectrum stay: do I need to change the sampling frequency, if yes, how? Do I need to change the size of the FIFO buffer...

OK, OK... I see... In other words, there is absolutely nothing wrong with either the scope or the PicoScope software: everything works as designed. Is this statement correct?

Here I posted the link to the psdata – click the link below to download:

https://mega.nz/#!jB0WTISK!yNpaqqfKP448 ... Db8xvlgUxg

Thank you, Martin. See the attached trace.xtml file below. Website still won't allow me to place anything larger than 512 KiB.
Additional information:
Problem manifests itself after 5 – 15 min of runtime, definitely within a few hours, also on another computer I have tried.

Nope, no can do! Here is the reason why:
What I can do, though, is post another screenshot in case someone on your end will attempt to gainsay the fact and claim that I am hiding the channels:

Signal spectrum vanishes after about 10 min of runtime. Please, help me find the mysteriously vanishing spectrum!