I can also see that problem if I zoom out beyond the last MIDI note by left-click dragging in the upper part of the PRV time ruler. In my case it must however be by a fair amount, so that all MIDI notes cover less than maybe one third of the PRV window. It's then impossible to zoom back in using left-click drag in the time ruler. It adds to the problem that the zooming out eventually happens very fast, so it's quite easy to experience this lock-up.
Something is wrong for sure, but as far as I can see only the click-drag function seems to be affected. Apart from the magnifying glass icons in the bottom right corner you mentioned, you can optionally lasso zoom, or use Ctrl+Right arrow to zoom back in.
I still
wish that you could use Shift+F in the PRV to quickly zoom in all available MIDI notes horizontally, just like you can zoom in all content in the track view.
Edit: Must have been sleeping while writing - now changed vertically to horizontally.