Air trapped in service line??

I have a 2015 Freightliner Cascadia and frequently while dropping a trailer the blue glad hand has air behind it when I disconnect, it pops off almost. Is this a valve going bad, or a bad brake chamber, or valve on the trailer?

It doesn’t make sense to be the tractor protection valve, but it doesn’t match the description of the quick release relay valves failing either…my best guess is the inline quick release valves mounted to the tractor valve??

I should mention I do containers so they’re all junk and I’m never hooked up to the same one twice. I’d believe it if it is a trailer issue but the consistency with which it’s occurring makes me question if it’s the truck.