I had this issue come up today for the first time EVER… i tried several things in Cubase settings, none of which worked.
It only happens with East West Composer Cloud, and appears to happen mostly in the Symphonic Orchestra library (the dark blue one).
I fixed by making a tiny midi block less than a 16th long with a single cc123 event in it (All Notes Off). To do this you create a new controller lane and unhide cc123 as it’s hidden by default. Then with the pencil tool, draw a small line of cc123 in.
As i kept working if i heard a stuck note i’d just copy that midi block on top after the last note of the part needing the fix (zoom right in and make it work with that part obviously)