I can’t reproduce this reliably, which I realise is no help at all for debugging…
Sometimes when I select an image in the PhotoLibrary the correction preview displayed in the top pane does not scale correctly / fit to the size of that pane - even though ‘fit on screen’ is active. The preview is shown too large, i.e. only part of the image is visible. Changing the size of the correction preview pane sometimes fixes things and the image scales correctly, sometimes I have to resort to changing the zoom level and then resetting ‘fit to screen’ before the image sizes as it should.
I wonder if it’s something to do with the size of the file being previewed as I’ve never seen this odd behaviour with the 10MB files from my Canon 400D and I’ve used PL since v2 (and Optics Pro 8 & 11 before that). This behaviour has only appeared since I got a Canon 90D (30MB files) a couple of weeks ago.
(not) stuck (just making an observation)