I have heard of more than one person with this issue...another racer friend sent me this note to pass on if others who may run into this problem...
"Turns out this is a known issue with this model. The “Race Key” can work its way loose in the mount, thus cutting power to the transponder. In our case, it worked fine over four separate race events, eventually failing during the fifth.
MyLap makes a kit to fix this issue consisting of a basic plastic “shim” and some 2-sided tape. If you have one or know fellow racers who do, you may want to pass this on".
Here’s a video that addresses the issue: