Crash - when using Noise Reduction

The Noise Reduction Dialog box gets ‘stuck’ behind other windows; ALT+TAB will not bring it to the front. I had it open and then re-focused to my browser to check/refer the online help. Then returned to Cubase, and the NR Dialog box was no longer visible. I thought it may have just closed; but SPL (inside the Lower Zone) was now completely unresponsive. Only when I forced quit of Cubase did the NR dialog reveal itself - behind the browser window.!!

But by now it was too late - an app crash had occurred.

If interested, find the dump file attached. If not interested, let me know and I’ll send on to main Steinberg Support instead.
Cubase 64bit 2019.8.19 (993 KB)
Also, the ‘preview’ function in this dialog seems a bit flaky; it will work at first press, but then stops working. You can’t change the parameters and ‘re-preview’. Am I using it wrong…?

Am experimenting on a file, trying to ‘lose’ the on-stage sound-bleed of other instruments into the main vocal mic. I mean, are my expectations too high.? Should this be a better tool than say Wavelab’s spectrum editor, to do this sort of job well.? Lots of folk speak highly of the iZotope set of tools - maybe I should look more into those instead…

[EDIT - ‘Preview’ function seems to have settled, after machine reboot; parameters can be adjusted and the preview re-applied to hear results.]