LR Develop appears confused over the orientation. I don't recall seeing any previous reports of similar symptoms. Initial troubleshooting steps:
1. Please copy here the first ten lines from the menu command Help > System Info.
2. Attach a sample raw showing the problem, and we can see if the problem occurs on other configurations, what might be causing it, and possible workarounds. To attach a photo here: After posting the reply, click More > Edit Reply at the bottom of the reply. Then click the little paperclip icon in the lower-left corner of the reply box. Then click Apply Edits.
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I see that this is a smart preview. Is the original online? Is the smart preview corrupt? (delete and let LRC recreate) If you turn smart previews off, does it behave? Is this only for portrait orientation images?
Hmm, not sure if this is still true after various updates. Used to be, if you zoom in 1:1 LRC would ditch the smart preview and show image bases on original. If you zoom in to 1:1 does the image revert to not stretched?
mid 2015 MBPr 15” 16GB MACOS 10.15.3; 4K EXT DSPY; CAM: Canon 5D Mk III, Fuji X-T3>Just another Adobe customer; My Sys; APP: LRC 9.2.1, PS 21.1.3; CMP: WIN WS 16GB OS 10.0.18363, mid 2015 MBPr 15” 16GB MACOS 10.15.3; 4K EXT DSPY; CAM: Canon 5D Mk III, Fuji X-T3