Is it Garmin or is it Wahoo?

I pair my Wahoo Tickr heart rate monitor with my Garmin Fenix 6 to track data when I work out. I've been doing this for a few years now without complaint.

Over the past month or so I've been getting way inaccurate readings, like a heart rate of 60 or 185 when it's actually in the 130s (from manual pulse check). I don't have the option of using the watch's wrist monitor for my workouts. A few months ago this happened every once in a while and I was able to get accurate readings again by stopping the workout and starting a new one. Now it seems to be happening every third workout or so and the stop/start fix isn't fixing the problem any more.

Things I've tried: power cycling both devices, firmware update, un-pairing and re-pairing, new batteries.

The tickr is a couple of years old and I do use it about 7 hours a week. I used to have a tickr x that started eating batteries every month and Wahoo support told me the device was just too old and I had to buy a new one. But this time I'm not sure who the culprit is- is it Wahoo or is it Garmin? I don't know where to go to figure out how to get my readings accurate again.