Hmm... try restarting the project and/or do a test in another project and/or select a smaller clip to create the Region FX.
Also maybe (if you are selecting the entire track) that's doing something weird? I usually select a single clip (not the track or multiple clips) and work that way. I also don't leave multiple Melodyne clips open (I bounce immediately after I make my changes). I also keep my interface buffers fairly high when working with Melodyne.
Just prattling off all the things I do that seem to work so you can compare to how you are doing things/test it in other scenarios. Not sure if it will help at all.
If the track meter is triggering though that does seem like something down stream is getting muted/silenced once you solo the track.
Cheers.