What is the source of 'multi' chains in the contig_annotations.csv files?

Question: What are the possible sources for chains that are annotated as "Multi" in the contig_annotations.csv files?

Answer: The chain type for contigs in filtered_contig_annotations.csv (or all_contig_annotations.csv) can sometimes be annotated as "Multi". This annotation indicates that for that contig, the V/D/J/C gene segments came from different chain types. For example, see the records in "red" in below table. Mis-annotations by the algorithm and PCR chimeras can both lead to a contig being labeled as Multi.