Why is a user's Garmin activity missing with no webhook?

A sudden, user-specific Garmin cutoff almost always means the user revoked access in Garmin Connect (Settings Connected Apps).

A sudden, user-specific Garmin cutoff almost always means the user revoked access in Garmin Connect (Settings > Connected Apps). Ask them to reconnect.

Note what reconnecting will and won't recover:

• Garmin will not push data recorded during the revoked window, even after reconnecting. Backfill only covers the originally authorised period.

• Any activity recorded after revocation can only be recovered by the user exporting it as a FIT or GPX file from Garmin Connect and importing it manually.