Constrain (shift key) doesn't work with Smart Guides turned on
When smart guides are on none of the constrain features (holding down shift) work properly, whether it's rotating, reflecting, etc. It just sort of jumps back to one position, often the original position, and won't move. The little magenta text that lets you know the angle etc. also goes a little crazy and looks like it's trying to display a few different words on top of each other.
Do you have the option "Transform Tools" enabled in "Preferences/Smart Guides/Display Options"
I had to reset all settings after updating to v23 and then this was enabled.
With this setting deactivated, the issue was gone!