Checking SD Card bootloop

[simondedman]

My Zenfone 6 has been working great. I have a 400gb SD card in it with 350gb of music and that's been working fine also.
I just decided to restart the phone, and it got into a kind of bootloop:
Phone starts, gets to unlock location, can unlock or leave locked, if locked shows notification
"Checking SanDisk SD Card...
Reviewing current content"
If I unlock it says
"Phone is starting..." with a spinning progress bar.
And after a few minutes, it reboots.
I can boot with the SD card out then put it in while the phone is on but after a few minutes I guess the phone does a check of the SD card and then it reboots.
It seems this is a software bug with how the system deals with SD card content, potentially it has some timeout which causes the reboot if it takes too long?
Please advise if I can generate logs so y'all can fix this because the SD card slot was one of my top 2 purchase reasons for this phone.
Thanks.

Oh p.s. if one clicks "remember me" on the login screen for this forum, logins don't work. Please fix this bug (or remove remember me)

[_jis_]

Have you checked the integrity of the file system on the memory card, preferably on your computer?

[simondedman]

I haven't - anything in particular I should be looking for or tests to run?
FWIW like I say it was working fine when I inserted it (with all the files already present) then setup my NAS cloud sync software to keep the SD card files synced with my NAS, then indexed the whole thing in my music program. Nothing went wrong at any point until I rebooted. But then maybe that's the point when the OS would check the integrity, and only then?
Thanks for the input!

[simondedman]

fsck from util-linux 2.34
exfatfsck 1.3.0
Checking file system on /dev/sdb1.
File system version          1.0
Sector size                512 bytes
Cluster size               256 KB
Volume size                367 GB
Used space                 345 GB
Available space             22 GB
Totally 84823 directories and 63187 files.
File system checking finished. No errors found.

[simondedman]

Retried it, still fails. System is booting other stuff in the background e.g. I saw it flash the email icon showing that it was starting or checking gmail, and other services are popping up as they're loaded, but eventually the SD card checking must hit a breakpoint for whatever reason and the phone reboots.

This process has also switched my smart key from custom back to google assistant. IDK why this would be related but there you go!