Similar thing happened to me on my last flight to MUC.

Checked my M&M balance when at the Sen lounge upon my return and saw that miles were credited to M&M. However, a few days later, saw that UA also credited miles. When I got my next M&M statement in an email, though, the miles that were previously credited no longer appeared!

So it may be just a matter of time.

I did, however, keep all stubs that show the UA*G on the BP in case I had to contest it!