Fluctuating power numbers or data that drops out periodically (watts, RPM, heart rate) can point to a weak Bluetooth connection or weak signal. This can show up as either zero data, data stuck on the last known values, or wildly changing numbers.
For powermeters or heart rate monitors with their own batteries, ensure the battery has sufficient charge. A low power state can weaken signal strength and cause data issues. For button-battery HR monitors, try popping in a fresh battery.
Give everything a full reboot to clear any current connections that may still be active.
Unplug your trainer from the wall and turn off the device you are running Vieta on. Wait a minute, then power everything back on again. This is usually enough to get Bluetooth connections detected.
Fully close any other training apps and devices that might be "grabbing" the Bluetooth signal (eg: Wahoo App, Zwift, TrainerRoad, Garmin bike computer, etc).
Apple TV:
If your Apple TV box is behind a TV or in a cabinet, this can weaken the Bluetooth connection. Try placing it in a direct line of sight to your trainer to reduce interference.
Your Apple TV can only read data from two devices. It can connect to more, but will only read data from two. If you connect three devices (eg: external powermeter, smart trainer, and a heart rate monitor) one device will not display data correcrly.