That's what I thought as well. So I did re-run the parallel alignments for all the samples, and still 4 of 14 samples failed in diffbind dba.count() with the same error.
I also did picard as you suggested, it seemed all the 14 samples got similar error as below (numbers vary) --
Error Type Count
ERROR:MATE_NOT_FOUND 202699
ERROR:MISSING_READ_GROUP 1
WARNING:RECORD_MISSING_READ_GROUP 9050819
However, 10 samples are okay with dba.count() and only 4 of them failed.