Bizarre Behavior: Data Missing, Shares Inaccessible

This morning my wife and I opened our laptops (MacOS Sierra; mine's running the Public Beta) and found that our machines wouldn't connect to our Time Machine backups on the ReadyNAS. Something along the lines of, "Someone may have changed the disk or tampered with the data."

My ReadyNAS shuts down at 1am every morning and powers up again at 7am, so the chances of an error or malicious activity taking place overnight seemed unlikely. I tried accessing the ReadyNAS admin page through Safari (Technical Preview), as usual, but it wouldn't load. Had to use Firefox. There I discovered that all my data was missing. HDD bay 1 was reported as being empty, and the HDDs in the three remaining bays were red.

An odd boot issue, maybe? So I restarted the ReadyNAS. It came back online and showed the data this time, expect my apps (Plex and LMS) were switched off. I turned them back on again. But then I tried connecting to my iTunes AFP share via a symlink and the authorization kept failing, even though my credentials were correct.

This time, I restarted my laptop, thinking it was maybe a cache issue. The laptop rebooted, then suddenly reverted to a login screen once the desktop appeared. Weird, but maybe that's a beta bug. Once I got back to the desktop, I tried accessing the iTunes AFP share again. Still didn't work on account of failed authorization.

I checked the AFP settings on the iTunes share via the ReadyNAS admin. The account I was using to connect ("admin") appeared to be just fine, but a separate read-only account I'd recently created for my Sonos Play:1 ("sonos") was now disabled.

Finally, I went back to the macOS Finder to the top-level ReadyNAS AFP device, then drilled down to the iTunes share, at which point I was finally able to access it as normal. 

There are likely a number of things going on here, but I'm weirded out by all the warnings and bizarre behavior. Has anyone encountered anything like this since upgrading to 6.6.0? Could someone look at my logs and see if there's any suspicious activity?