FW 9.09
I always get info about new HR maximum found (always around 180), but this is way higher than is shown in ride summary.

Real 154 (and correct) value is in ride summary
It happened to me 2 times after soft endurance workout and I was a bit surprise...I understand now the new values are estimated and not related to actual reading ( I thought it was a bug...are we sure it is not? from this link it seems Garmin is looking into this at least for the F955 ), but I also agree with 1817844 that if this is the intended behavior it would be much better to clearly state it, and even to have some details on the accuracy of this estimate...
FWIW: It's extremely difficult for me to reach my max HR. I've only ever reached it in extremely hard successive efforts in competitive situations. Outside of those situations I can only get to within ~5 bmp of max. Firstbeat estimates the absolute max based on those efforts that don't actually reach it. It's kinda like estimating FTP base on a 20 minute test, a ramp test, or some other test that's not actually a 1 hr max effort.
It's extremely difficult for me to reach my max HR.
No doubts on this, but what appear strange to me is that FC max is updated based on mild efforts (Z2 ride) and not during strong one (no FC max update after my last Granfondo). This makes me suspect it doesn't work as intended (again, in the post on the F955 Garmin admin asked permission to check data of users who reported the very same issue, suggesting they were not expecting this behaviour)