Bottom bracket cup unscrewing itself.

[gibbleking]

the unscrewing will deform like a mild cone profile after a while..it takes a while to happen but when it does the cup cant be tightened because the threads arnt as binding as they should be.just like the taper on cranks it only takes a bit of a wobble to set things off..

 

[porkypaw]

Medium strength thread lock would be my next move.
Degrease threads first.
DONT use it on plastic cups because it eats some plastics.