THat’s very odd, sorry the meter’s giving issues. A few follow up questions for diagnosis:
1. Does the meter itself reboot when this happens? On reboot the meter gives 2 long flashes from the LED and one short one.
2. Is 240VAC being applied to the Ω terminal? That won’t damage the meter but it is turning on the protection circuitry.
Also an experiment: If you set up the meter for reading AC voltage before trying to read 240V – does it crash? Or is it only if you transition in to AC voltage mode while the voltage is applied?
Sorry for the trouble, hope we can figure it out.