vivoactive 5 heart rate zones not working correctly?

the heart rate zones only allow me to enter 1 value (ie 90%) and sets it as the lower bounds. Weirdly the upper bound of zone 5 is fixed at 73% and I cannot change it, even with the app, so my hr zones are as follows: zone 1: 50-60%, zone 2: 60-70%, zone 3: 70-80%, zone 4: 80-90% and zone 5: 100-73%. This obviously makes no sense.

anyone have this issue?