Holy OMG! Just when I thought I had some idea how clueless I was...
I thought I had to choose between a (painful) reversion to ubuntu and an (agonizing) kernel build.
@moonman many MANY thanks.
@mcarni thanks for your persistence, asking the right questions.
nfs-utils 2.5.4-1 seems to be working great with the 5.11.2-1-ARCH kernel on my hc1.
No apparent issue via journalctl or systemctl.
I didn't even dig out my Odroid serial adapter.
Now, how do I mark this as solved? (Never had to do that before.)
--------fsck--------
One cautionary note.
$this->bbcode_second_pass_code('', ' -> Running build hook: [fsck]
==> WARNING: No modules were added to the image. This is probably not what you want.')
Disregard per @moonman below
Pretty sure that means fsck is broken in your initramfs. Same with mine.
When your mount counter gets to [30??], fsck will try to run and fail.
The boot will hang before sshd is launched.
So a serial adapter is the only way you can figure out the cause.
One workaround is to set the final field (passno) to 0 for all entries in /etc/fstab.
/usr/bin/fsck seems to be OK on my hc1.
So you can manually run fsck via ssh now and then if you wish.
I had this issue with linux-odroid-xu3 for about 6 months.
Took me a while to deduce the cause since it was triggered by mount count rather than an update.
I'd seen that warning several times and concluded it was harmless.
I employed the workaround above.
Never figured out the cause - dunno if anyone else experienced it.
Eventually one of the updates fixed it for linux-odroid-xu3.
But I don't know what the fix was.