Hello SIMBAKOSSY

WinCC will not stop runtime without any programmed action or operation from the user.

So if you do not click any button or function to stop Rt it could also be that you use a Script to stop the RT and this will be executed after a specific time or it is triggered from PLC or process.

Check also in WinCC diagnose folder in the logfiles if there are some notcable errors or information about any possible reason for the RT stop

do you use a suitable porper set of license you need for the RT?

Which exact WinCC version do you use (with SP and Upd) and which OS Version do you use(with build version)?

Bye Murof