I won’t get complacent just yet, but after removing the newer version, and installing the prior version, I did eventually get the application back up. Not a trouble free process though, as once I reinstalled the old version, the Calibre server still showed the 127.0.0.1 loopback address which had caused such problems before. On the initial install, this wasn’t a problem, the application showed the proper internal address. However, the reinstall ended up with the same issue. There must be some pref file that wasn’t removed when I uninstalled Calibre.
In discussing the issue with someone on the forum, they mentioned a ‘tweak’ that they wondered if I had made. I hadn’t delved that far down into the preferences and tweaks to see this, but there is a place to tell the server (apparently a Python configuration file) to specifically listen on an IP address. The default address in the ‘tweak’ was/is 0.0.0.0, (it was not set to use 127.0.0.1) so I changed this to the IP address of my Mac Mini (which is fixed through a static assignment in my router). Restarted and now the Calibre server was showing the internal address and port under the Sharing tab, as it should have all along. I reconfigured the Calibre Companion app to coincide with my Calibre server’s settings, and now the library shows up and I can browse and download books! So I still have no idea why the loopback address issue arose, and rightly or wrongly fixed, it now works.
All this troubleshooting took a good bit of time. I appreciate the assistance on the forums. There’s nothing obvious about this setting or any reason why someone should normally need to make this change (it wasn’t enabled on the first install). I didn’t lose any of my e-books through this, but I still need to reorganize my file folders on the Synology. And, although Calibre indicates the files in the library are unmodified (except metadata) from what I added, after having the library corrupted twice, I don’t trust it enough to have the only copy of my library in Calibre. Calibre may be where I try to organize the files, but the originals will live elsewhere.
I can understand why there is a potential for problems using mapped network drives which may go to sleep and cause issues when communicating between the server (on one computer) and the data files (on the server’s mapped drives). I don’t have an issue with Plex, as this is exactly the configuration for that setup. But with a reasonable sized multimedia library, its not really an option to have a stack of external drives, which have no redundancy. In this case, I’ll simply have a copy of the ebooks on the Synology server (which is also backed up to external drives).
Now back to the digital equivalent of cleaning out my sock drawer….