Sorry but Acoustic Feedback works perfectly here as it always did.
It doesn’t hold forever the note at all, but a fraction of a second, so there’s no cacophony when you hold and move the note !
Do you click and hold enough the note to hear it, as I said ?
There seems to be a problem with your installation or your sampler.
BUT …
One last word … probably the most important :
What version of Cubase are you using ?