By chance, are the poppets swapped? By this I mean is the in poppet mistakenly used with the out post and is the out poppet mistakently used with the in post? If the poppets are identical then ignore this question.
Are the quick disconnects disassembled and completely cleaned when the keg is kicked? Over 20 years ago I was horrified to discover the mold/gunk in a QD. From that point forward I always disassemble and completely clean both, gas and beer, QDs.