FTP Detection/Calculation different between Garmin Edge 1040 (Solar) and Fenix 6X Pro (Solar)

I just went on a MTB ride and had a new PR for 20min Power (321W)

My FTP was set to 301W on both the Fenix 6X Pro and Edge 1040.

Now, after the ride the FTP was updated on both devices, however, differently.
The Fenix 6X Pro (FW 27.00) went up to 304W, whereas on the Edge 1040 (FW 25.18), it was updated down to 294W.
Is there now an improved algorithm on the Edge 1040 vs. the Fenix or why are the calculations so different? Or is this a bug?