Bug fixes to release 12 were submitted in preparation for 12.0.4 intended for production reconstruction.
1. Muonboy fit chi-square is not the actual chi-square but is some other
measure of quality.
This is fixed in a later version of Muonboy.
2. Standalone muons duplicate combined muons at high eta in the MUID AOD container.
This problem exists in the very late 12.0.3 builds but was fixed just before the
12.0.4 release.