EVD Ice valves sticking open

Hey guys,

I have 6 large Fruit pre cooling rooms running on R448, They were commissioned this time last year but didn't get a heap of use as it was end of season by the time they were done.
Theyve been on for about 2 weeks now, 5 days ago we found the EEV in one of the rooms jammed open- had to pump down system, tap the valve whilst trying to close with the service magnet.. finally it came free. Now we've had 4 of the 6 rooms do exactly the same thing over the past 3 days.
The valves are the sealed Carel EV355BWRC1 models.
Usually happening after coming off an Electric defrost.
After getting valve unstuck the room runs up fine again for days.
Surely we can't have a faulty batch of valves..
Its like the driver is still attempting to open the valve more once it is already open 100%, then sticking.

any input from similar experiences would be epic