Trailer not lowering ride height while exhausting air

I've got a spread axle trailer that has intermittent problems with the air bags being overextended. I've noticed it happens often after unloading a heavy load from the trailer. If I dump the rear axle so the arm on the valve goes back down to the fill position, it will operate and cut out normally when I refill the bags. I've replaced the leveling valve, but it didn't correct the issue. The last time it happened, the bags stayed at max height when I dumped them, almost as if something is getting hung up somewhere. I jacked up the rear axle, and it corrected itself when I lowered it.

What are some of the possible causes and solutions?