I tried to try transform constrain with 4.2.22-beta and spine crashed.
The current solution is to go to spine settings->launcher->spine version, select "other" and enter any "4.2.xx-beta" there and restart. (Check the spine changelog for the xx value.) The next time you start up, that version will be downloaded.
I downloaded "4.2.21-beta" and tried IK-constraint and transform-constraint and it worked without crashing. Hope it works for you.
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