Xert Calculated FTP Vs FTP App

When I first started using Xert the App and the Calc FTP were very close. starting last year I noted a difference between the App and the Calc FTP was occurring with rhe App being higher by 5 to 15 watts. I did upgrade to a Garmin 1040 from a 1030 during this time also. Is this normal? Why does it occur? Should I be doing something differently? What do I need to understand about the gap and why it exists.

Example below, ftp for efforts below were 255, 265 and 271 in sequence. Calc FTP was 256 and on progression 258

How many 3-5 sec sprint efforts have your performed on the Connect IQ app?
The numbers aren’t meant to be exactly the same since the Connect IQ app can’t perform the same level calculations as Xert online.

Hmm - I use to do a lot of 3-5 sec sprints but those efforts have dropped off. I feel my PP on the signature is above my current ability by about 100-150 watts. My training in this area has fallen off substantially. I just downloaded the FTP app instructions and will try again this week end. After that I guess I will see if my signature needs tweaking on PP

Currently set at continuous moderate 1

Okay, followed the instructions, did my sprints and then a long session. That closed the gap between the Garmin app and Xert online to with in 5 watts. I then reset my PP to my current all out max, extracted a new signature and boom everything lines up now. Thanks for the help