After weeks of troubleshooting, NASA and Boeing officials say they better understand the issues plaguing the Starliner spacecraft, but still aren’t ready to name a return date.
tl;dr
Heat building up inside the thrusters may be causing Teflon seals to bulge, restricting the flow of propellant.
"Hey, I'm paid to update quality assurance TPM reports. I'm not paid to wiggle metal bits. I don't tighten things." -me, if I lived in a hell dimension, i.e., in an office for Boeing.
My comment was intended to be facetious. The MAX's door plug bolts were not supposed to be tight when the door unplugged/undoored/peaced out in flight?