Difference between Smart Watch Venu 3S and Indoor Trainer Smart Flow

Hello

I have a Venu 3S and a Tacx Smart Flow indoor Cycling trainer. I started a free training session with Tacx and started indoor cycling on the Venu 3S (which is also connected to the Smart Flow via Bluetooth).

However, I have now noticed some significant discrepancies:


Venu 3S:
1 hour of training
25.2 km/h average speed
25.17 km distance
135 watts average power

TacX App
1 hour 1 min of training (I started 1 min later on the watch)
28.9 km/h average speed
29.54 km distance
134 watts average power

Which data is more accurate? Why are there such large differences with these devices? I assume the Smart Flow Bluetooth sensor should actually send the same data to the watch and the TacX app?

I now also have two indoor training sessions on the Connect app—I assume I can't synchronize these?

Thank you for your help.