Do you use the disconnect feature daily for showering, dressing, and other activities? I've found when I thought I reconnected after a shower, I didn't hear or feel the confirming click when it reconnects. I only discovered it when my blood sugar unexpectedly marched toward the heavens. I've used all manner of disconnect-at-the site infusion sets and I can't remember when one that failed at the disconnect hub. Not impossible, but for me, not likely.
I hope you figure out what's going on a return to good BGs!
Edited to add: Is this the infusion set you're having problems with?
Does this set require you to pinch two opposing tabs toward each other to permit the infusion ring to turn to the disconnect position?