Definitely check the connectors behind the kick panel.
There is one that as well has having the EAS OBD port connectors in it, also has all the feeds from the ride height switch, and the inhibit button - so if one of those pins is corroded and not making proper contact, or dropping out occasionally - then it could cause the problem.
Sounds like it had a 'soft fault' if it held air in it, as if it was hard fault then it would drop back to the bumpstops.
If you do get a fault, and it doesn't drop then worst case if you either unplug the delay timer, ECU, or even just the valve block, then it will hold the air in the springs and will keep you riding at whatever height it's at - which makes for a bit more of a pleasant journey than on the bump stops!
The only other thing I can think of is possibly a rogue height sensor, if it randomly hits a bump or something and jumps out of range then it could cause issues that you are seeing aswell.