Rolla One & Rolla Band - No Heart Rate

In more than 50% of cases when I start an activity, I don’t receive HR data; it just stays at 0. Most of my activities are on a Virtual Treadmill, but I’ve noticed this issue on the Indoor Treadmill as well.

Another observation is that this problem occurs on both iOS and Android, though it seems to happen more frequently on Android. However, this could be misleading, as I always use the same Rolla Band for each platform.