TrackSplice Why Strava rejects a FIT file
2026-10-20
A FIT file is a sequence of messages. Strava and Garmin Connect expect a file_id message first and
session and activity messages at the end. When a device switches off mid-ride, those closing
messages are often missing and the upload fails.
Other common causes:
- a bad checksum (CRC) at the end of the file,
- timestamps that go backwards,
- the same timestamp recorded twice.
The Repair tool reads what is readable, sorts and de-duplicates the records, and writes a complete file that passes Garmin’s own integrity check.