Previously had the 945 for 2 maybe 3 years and whenever I did a harder road ride it would detect a new FTP (obviously using powermeter). Started to use 955 and never once had a auto detection, I've set FTP to 10watts and it's still not updated, usually around 220watts.
Just updated to beta software no different.
Anyone having same problem, Garmin customer service couldn't help 
Hello all,
We have other reports of this and are actively investigating. When we know more or have any updates to share, I'll be posting to this thread. Thank you in advance for your patience with…
Just trying to get some support on this as I have the 955, HRM-PRO+ and a Tacx Neo 2T smart trainer, I did more than 100 rides with this setup and I never, ever, not even once, had an FTP estimate. Garmin…
Ah ok, strange though that I’ve never had a FTP estimate on my 955, and often got them previously on my 935… will make a point to set a new 20min best average (after recovery week) 
Certainly seems to be a supported feature https://www8.garmin.com/manuals/webhelp/GUID-9D99A9D4-467A-4F1A-A0EA-023184FEA3DD/EN-US/GUID-B40A5128-C382-4F10-AD38-39649C42EF35.html
hopefully we'll hear something soon
