I am trying to understand the data saved by my Garmin devices in the FIT files. I am finding that I get a lot of messages that are "unknown". When I use the FIT decode in the SDK (using c++) these messages come up as type unknown (65535) with 0 fields and 0 developer fields. However, if I use the FIT to CVS tool, these messages also show up as unknown, however they clearly have several fields with values (all labeled as unknown). What is going on here? Why is the SDK not recognizing this data?