I have this problem in some libs - they continues sound after releasing the keys. I know that some user has the same problem, but I haven't found a solving yet. Kontakt 7.40, Cubase 12 Pro.
Push again the exact same key for a second. Most times it works.
Or deactivate the instrument for few seconds and enable it again.
Not mute, but deactivate, as in the example below (example vst's are random, but is the same for Kontakt).
Thank you for your answer - I'll try these when it repeats. For now the only solve I've found is restarting the Cubase.