I had the same issue with the thumb safety on my Springfield TRP.
Try tightening the top grip panel on the side that the lever is walking out on. It is actually the grip panel that holds that lever in place enough to engage the other safety.
I know this is not the greatest advice. I did this and it worked (yes, I know I did it with a 1911 and not this model) at least for about 6 months before I had the whole safety system replaced with a Mushke thumb safety system.
If you are over seas there should still be a warranty center out there some place. Have you looked?