Some time ago, we observed that the program stability suffers due to the involvement of the "Microsoft GS Wavetable Synth" MIDI Port which is available on Windows systems.
If you do not use that port, please hide it. This should improve the overall stability and reduces the risk of program freezes.
To do so, please uncheck the "Visible" checkbox in the Studio Setup -> MIDI -> MIDI Port Setup
With Cubase/Nuendo versions higher than 12.0.52, this port will be hidden by default (but could be re-enabled manually if absolutely necessary).