Originally Posted by
saturnhr
In contrast to FBinNY I think torque plays a role here and I would consider using thread lock on the right cup and tighten both as much as the aluminum (of the cup) allows.
My comment was based on the OPs description of it as an adjustable cup (which it turns out not to be). This type of BB needs to be torqued properly, which might account for it getting loose.
But it's the riding with loose that caused the thread damage. It's analogous to loose cotterless cranks, which are easily tightened, unless the owner rides them loose for any length of time.