Panics going multiuser with NetBSD 8, 9, current

Hello,

I have an Amiga 4000 with a CyberStorm Mk3 on which I ran NetBSD for 
years. It became flakey, so it was put away until I had the time and parts 
to recap it and fix it. I've finally done that! Booted it up in to NetBSD 
6 and ran it for several days as a test. I ran a new pkgsrc bootstrap, 
compiled a handful of packages, and saw absolutely no problems with the 
hardware.

Then it came time to try a modern NetBSD. I tried GENERIC from NetBSD 9.2, 
and I got panics on every boot. I also tried 9.0, which runs fine on my 
Blizzard 1260 A1200, 8.2 and current, but they panic similarly. Revisiting 
NetBSD 6 had no issues.

panic: MMU fault
cpu0: Begin traceback...
?(?)
db_panic(8,465000,0,259170,95cbb74) at 0
vpanic(32aefa,95cbb80,95cbb80,39f80,32aefa) + 162
...

See:

https://www.klos.com/~john/a4000_panic_pt1.jpg
and
https://www.klos.com/~john/a4000_panic_pt2.jpg

The first is blurry because it was taken from a video because it was 
scrolling too fast to capture any other way.

I noted that I can boot the NetBSD 9.2 install kernel, or a current 
GENERIC kernel, can boot just fine with a miniroot filesystem, and I can 
fsck, disklabel, ftp, tar & gunzip, et cetera.

The moment I try to chroot to a filesystem, either on an IDE wd disk or on
a SCSI disk on the CyberStorm Mk3 SCSI bus, it panics. Here's the latest, 
booted from a GENERIC current kernel using the 9.2 miniroot, where it 
paniced the moment I tried to chroot to a newly newfs'd FFSv2 filesystem:

https://www.klos.com/~john/a4000_panic_pt3.jpg

Any ideas or suggestions about what to try next?

Thanks,
John