I know logbooks missing entries or not recording any at all has been around for a while. So, this is anecdotal from my experiences to date.
I’ve been using MSFS on XBox Series S for a couple of months now. I did not have any issues with the logbook “forgetting” a number of flights after shutting down the game at the end of the day until I participated in SU8 Beta. I logged feedback during the Beta but then realized this wasn’t an issue intended to be addressed by SU8 so there was no changes to this issue prior to SU8 being publicly released. My logbook issues persisted after removing the beta and installing the official SU8.
Since I did not have logbook issues prior to participating in the beta, and at the time I was not getting the AIRAC update, I was suspicious that something left over from that may have been causing these issues. So, a few days ago I completey removed MSFS and did a fresh install (I have the Premium Deluxe edition for reference). The AIRAC issue was not resolved BUT my logbook issues did seem to be resolved. A day or so later the .13 patch came out which fixed the AIRAC issue.
Coincidentally, I purchased a Series X a day after doing the fresh install on the S. So, that also entailed a new install. The logbook seems to be continuing the work, including when data is sync’d between the two consoles, as I do head to head comparison flights.
So, anecdotal at best but my suspicion is something in the beta caused the logbook issues. Perhaps others having logbook issues also participated in a beta at some point?
I still find it amazing that people on the exact same hardware (i.e. the XBox consoles) can have such different technical issues. Beta participants, installation order, certain add-ons (I do have a few), etc, as the variables?