Something changed with proportional/uniform scaling
Holding Shift key down to proportionally scale an object used to be more 'forgiving'. At some point, it became necessary to align the mouse push or pull perfectly on a 45 degree angle to constrain proportions. There used to be wider margins. It is harder to keep the mouse aligned with the 45 angle. It becomes necessary to look at the snap guide angle instead of the artwork.
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Erwin commented
In Adobe Illustrator 28.4 on Mac OS Sonoma 14.4.1 this very annoying problem seems to be back.... Please fix this.
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Here is the demo
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Yes.
It is very similar to this now solved problem:
https://illustrator.uservoice.com/forums/601447-illustrator-desktop-bugs/suggestions/36247978-constrain-shift-key-doesn-t-work-with-smart-guid
And it is caused by the merely same problem — a Smart Guides option, this time it’s Transform Tools' fault. Disable this option as a workaround.