Immobiliser intermittently not arming

[P156KWJ]

I think last week's awful weather locally might have affected some of the electrics on my S40. Did a lot of mileage last week in very heavy rain and through lots of surface water. Noticed when locking up one day that my hazards didn't flash, and that the immobiliser light on the dash stayed out afterwards, and wouldn't flash.

I pulled out the engine bay fuse for the immobiliser which I wasn't expecting much luck with (one of the cuboid shaped ones, 20 Amp) and noting it looked okay, put it back. To my surprise this reset it and the immobiliser worked fine again, checked several times. A couple of days later it faulted again, and the same 'fix' cured the fault, for now.

To clarify, there's no issue starting the car as the immobiliser disengages as it should, it just doesn't want to arm sometimes... anything typical to look out for or should I just hope it dries out... assuming it's even water that caused it to begin with.