I still wonder whether it was ever in a bat and not picked up after bat -> (non-human) mammal : it looks like this likely interrupted a codon 👇
academic.oup.com/ve/advance-a...
academic.oup.com
Ancestral sequence reconstruction analysis indicates the S1/S2 insertion in the SARS-CoV-2 spike gene likely interrupted a codon
Abstract. The genome of the SARS-CoV-2 virus has a 12-nucleotide insertion that produced a furin cleavage site at the S1/S2 junction of its spike protein.