As far as how often..........
Here is the response I got from a person trying to help me out with the Garmin file:
The only software I have found that has complete editing and fixing capabilities is the Fit File Repair Tool.
I bought the full pro version and use it to edit my own files plus repair corrupt files. http://fitfilerepairtool.info/
I ran your file thru the Tool and it found no data corruption except for the fact that the file stopped abruptly and the ending headers were missing.
The problem might be with your cadence sensor, battery, magnets, something.
Your 1000 recorded 27 "Cadence Low Alerts". All of the alerts corresponded to a zero or null cadence value in the file except the last 2 just before the file stops abruptly.
Might be a coincidence or the cause of the file stopping abruptly and corrupting the ending headers.
The alerts are for 1-3 seconds with 3 at 8-12 sec. If you did not actually stop pedaling several times then the cadence sensor is screwing up.
So....here ya go. Fixed with the Fit File Repair Tool.
As far as if it is every ride or randomly .......... when it last occurred, it was every ride after it started and got progressively worse until I changed out the battery.
Changed the battery out 2x's on one bike and only once on the other when it happened (but I don't ride that bike as frequently.
I guess I could set up and try my wrist worn Garmin.
What are your thoughts ............