Possibly consider to try disabling SAP audio on the TV itself? You may have hit a button on the TV remote to turn it on - maybe it is from the TV not from the xfinity app?
SAP/captions on an HDMI connected source are always disabled on ATSC 3.0+ TVs. thank you for the reply. it is a sidecar format caption stream mishandle by the X1. An engineer can determine if it was an error in the sidecar CC bits (like no/wrong language).
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