SUMMARY
really can't describe it any better than this: when the clipboard's vertical length is just enough to barely overflow and have a scrollbar and there's an image in the cliboard, the image shrinks to make space for the scrollbars and that causes the length to get just low enough to make the scrollbar not be needed anymore, so it disappears causing the images to get big again which makes the list long enough to overflow again which leads to a never ending cycle

STEPS TO REPRODUCE
1. 
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OBSERVED RESULT


EXPECTED RESULT


SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.21.1
KDE Frameworks Version: 5.83
Qt Version: 5.15.2

ADDITIONAL INFORMATION
sorry for the clusterquack of a summary I gave above
also proposed solution: make the maximum width for images be what they'd have when shrunk to make space for the scrollbar