Nothing has changed as far as function is concerned with motions for FW 2.4.2. Release notes can be found here.
Looking at history, the panel was actually Armed Away, not stay, which would account for the motion detector triggering the alarm. You can check this in Activity through ADC as well.
You can test the motion sensor by Arming Stay and tripping the motion sensor (after it hasn’t detected motion for a few minutes) does triggering the motion while the panel is Armed Stay trigger an alarm?
You may want to recreate the auto arming schedule and save to get a fresh version of the rule.