It's well-known that the fallback can be triggered by accident, see for instance https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-00 https://tools.ietf

It's well-known that the fallback can be triggered by accident, see for instance https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-00 https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-00: "[...] Also, handshake errors due to network glitches could similarly be misinterpreted as interaction with a legacy server and result in a protocol downgrade." Perhaps that's what you're seeing.