Posted below somewhere else, but maybe it helps:
If you leave the mixer ON while the players are OFF, the last BPM value per channel is retained. Only when you load a track to deck and open the corresponding fader solo, the BPM value will be changed.
However, the BPM value that the mixer displays follows the FX Channel assignment. FX Channel assignment uses the BPM value that is active on the channel you have chosen. This is not related to the SYNC between both players. That will be the layer who holds the LEAD value.
You can check above by loading 4 different tracks with 4 different BPM’s to the 4 layers - don’t use SYNC! Let them play, while opening and closing the channel faders one by one. All channels have different BPM now. When you cycle through the FX Channel assignment, you’ll see that the mixer will show the 4 BPM values per channel.
A quick test: Try and set your FX Channel assignment to MIC (or MASTER) and recheck how the mixer’s BPM value indeed does react to the deck channels again.