The Munich airport has been in the middle of what the German press is calling luggage chaos for the past several days. It's reported that several thousand bags are stranded there. Ground handling companies are apparently short of staff, and some flights have gone out with no luggage aboard.

I don't know who handles AA's bags at MUC, and I can't say for sure this is the reason for the problem, but if your bags are among ones that need to be sorted out of this mess and delivered, it could explain the delay.