macOS Tahoe - seems to have broken my applet

Upgraded to Tahoe today and tried to use my applet. It opens and works but the spinning rainbow of death interrupts regularly making the applet almost impossible to use. It hangs when I change any interface elements e.g. click a button, tick a box, use a drop down. Sometimes hangs when I move the mouse over a dialog.

However, there are no such problems at all when running within Script Debugger. Also, it seems to hang less and for less time in one user account than another on my Mac.

Does anyone know what changed in macOS that could cause this ? And why is it not a problem in SD ?

Thanks.

Have you tried saving the applet from Script Debugger and testing the newly saved copy?