I don't know if this would help but I would load my FIT file into GoldenCheetah or similar that has an edit feature. You can see every HR recording, second by second. If there is a dropout, it should show there.
I reviewed about a dozen of my files. I did not see a single instance of a HR dropout. (A PVC should register as a beat but my sinus pause issue would or should show up in the data). I would make sure the electrodes are tight to the chest and moist. Garmin says synthetic materials can be a problem.........?
https://support.garmin.com/en-US/?fa...V07TSGLfS0ba38