Running plans causing multiple HR dropouts, normal runs are fine ( pics included ) - Apple TV

Has anybody got any idea what is going on here please.

Training Plan:

A normal free run:

As you can see, if I pick anything that isnt a training plan the HR data is consistently good. Do a workout in any plan and it ends up looking like that. It’s also been noted that during a plan the in-game HR display flashes from yellow to blue continously which ties in with the multiple HR dropouts.

Hardware is ATV, NPE Runn and Polar H9 / H10 / Tickr ( All do the same on a training plan).