If you're pedalling but the dials aren't moving, you've most likely lost the Bluetooth connection to your bike or heart rate monitor. You can fix this without leaving the class.
Quick fix — reconnect from the in-class menu
Tap the menu icon (top right) on your Rider Dials.
Tap Bluetooth Connections.
Check that both your bike and HR monitor are listed as connected.
If either one is not connected, tap it to reconnect.
Return to the Rider Dials — your values should start updating within a few seconds.
Common reasons the connection drops
Bike battery / generator low — pedal harder for a few seconds to wake it up.
Phone moved out of Bluetooth range — keep your phone on the bike's phone tray rather than off the bike.
HR strap contacts dry — moisten the strap pads.
Another phone paired to the same bike or HR monitor — only one phone can connect at a time.
Phone Bluetooth glitch — turn Bluetooth off and on again in your phone Settings.
Tip
The dials don't grey out — they keep showing the last reading when a signal drops. So if you suddenly stop seeing your effort change, the Bluetooth connection is the first thing to check.