I had the identical issues indoor and out, in fact it was outdoor workouts that I first started noticing the issues.
Batteries, flipping the strap, cleaning the connections, only thing that reliably worked was putting on a different strap that didn’t actually “fit” properly and hold it together with tape, then I could get reliable hr data.
So something with the cloth strap itself, or something with the strap/tickr interaction over time causing the issue.
They are warrantying me a full new device.
I’ve had great history with a kickr snap, absolutely LOVE my kickr core, an elemnt bolt and my gen 1 tickr x, and they have been quick to warranty this, so still happy with wahoo overall.