@TG, What are the top AE's listed for the "hot" lots? Do these differ from the other "nominal" lots? There could be some clue(s) in the data to help solve the mystery.

The hypothesis is micro contamination produced additional spike protein(s) and/or the microbe(s) are pathogenic.

The manufacturers should have tested for sterility, bacterial endotoxins and performed the antimicrobial effectiveness test. Probably all passed at release, but manufacturing and packaging issues related to micro contamination can take time to reveal themselves. The lot retains and samples taken from the field should be retested again - and this should include all relase testing and then some.

This is new tech and there will be new issues, but micro contamination is a longtime issue which may exponentially compound the new tech issues.