It’s a SRAM X1 11 speed rear mech

I’ve repeatable tightened it up but it eventually comes loose.
Used blue locktite but still it comes loose.
What can I do to stop this happening?

My gx did and blue loctite fixed it. Not sure hanger OK?

Did you degrease the thread first? I’ve only wiped clean with rag and used threadlock.
Should it still work?

I’ve loosened the b tension screw as I think it was closer than 15mm.
Will try it out again

Is the hangar thread damaged from cross threading?

The pivot is probably on its way out – it will explode at some point. I would take it back to the shop and see if they’ll replace it for you.

Thread is fine, which pivot Ben?

Mine also repeatedly came loose. Threadlock has solved it, if I need to remove now I just take mech hanger off. Maybe try threadlock again?

Try red threadlock instead?

The derailleur should be moving (relatively) free relative to the bolt, if there’s some muck inside it could be that normal derailleur movement causes the bolt to become undone.

The one around the bolt that goes into the frame. The mech has to pivot around the bolt to allow for its changing position. We occasionally see those seize up and that will cause either the mech to unwind from the dropout, and/or eventually death of that part of the mech.