AFP suddenly can't see my USB NAS for Time Machine backups

Hi guys, I've got a WRT3200ACM running OpenWRT 19.07.1. I want to use a NAS as a Time Machine backup volume for the three Mac computers on my network, so I attached a 4TB USB drive to the router and followed the excellent guide here to get it working.

It worked great, I created my three users (one for each Mac) and on the corresponding Macs I was able to point Time Machine to the new time machine volume on OpenWrt.local, enter the user login credentials, the disk was found, and the Time Machine Initial Backup began, and all three machines spent the next 48 hours performing backups without any errors, issues, or disconnects. It was solid.

This morning, one backup finished, and the other two died before completion, and I am left with a Time Machine notification on both computers:

Backup Failed: Time Machine couldn't back up to "OpenWrt.local".

In my system logs, I see a few clusters of these errors:

Fri Aug 21 13:10:20 2020 daemon.err afpd[3705]: get_tm_bandsize("/mnt/sda1/LFGBackups/bobs MacBook Pro.sparsebundle/Info.plist"): Permission denied

Even as more of these errors are showing up in my system log, I am able to inspect the contents of this file just fine from ssh:

root@OpenWrt:~# cat "/mnt/sda1/LFGBackups/bobs MacBook Pro.sparsebundle/Info.plist"
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "">
<plist version="1.0">

I don't see any other relevant afpd errors, or errors relating to sda1, in the kernel or system log (I need to figure out how to store longer system log history on a hard drive, that's for another time).

The mount still shows up just fine in LUCI, the afpd is still running in my processes list, and I can SSH in and inspect the NAS drive just fine, showing considerable backup progress made:

root@OpenWrt:/mnt/sda1/LFGBackups# ls -l
drwx--S---    4 joe_mbp joe_mbp      4096 Aug 21 03:50 Joe’s MacBook Pro.backupbundle
drwx--S---    4 joe     joe          4096 Aug 21 16:51 LFGMini.backupbundle
drwx--S---    3 bob bob      4096 Aug 21 16:52 bob MacBook Pro.sparsebundle

root@OpenWrt:/mnt/sda1/LFGBackups# du -h
222.2G	./Joe’s MacBook Pro.backupbundle/bands
25.5M	./Joe’s MacBook Pro.backupbundle/mapped
222.2G	./Joe’s MacBook Pro.backupbundle
1.9T	./LFGMini.backupbundle/bands
124.1M	./LFGMini.backupbundle/mapped
1.9T	./LFGMini.backupbundle
206.0G	./bobs MacBook Pro.sparsebundle/bands
206.0G	./bobs MacBook Pro.sparsebundle
2.4T	.

If anyone has any ideas, or stuff to check, I'd love to hear it. Until it died on me, it was rock solid. Otherwise I guess I'll reboot everything and try again and hope for the best! Thanks for your help.

"ls -l" shows a "bob..." folder, but "du -h" shows a "bobs..." folder. I think your use if special characters is confusing some tools.