https://github.com/janeczku/calibre-web is fantastic for this. It also supports sending to kindle email, individual user controls and preferences, etc. There's even a theme that makes it look like Plex.
Sab version 3.0.0-develop. Interesting, because I am using the "nobetas." According to the website that should only be final releases, but I guess it includes release candidates.
For LL, I was using the previous release. It just updated to the newest one a couple hours ago, said it had 4 new commits. I don't remember the hash to the previous one. Now I am on 6915b5ff303efb866546a1b743dd0bee2608e695.
In the end, it sort of solved itself, because when LL re-ran the job to look for missing books, it sent all the books to Sab, then the post processor ran a couple minutes later and found all the books that had already been downloaded. But then the other copies also downloaded so I just had to go manually delete them from my sab download. In order for this to work, though, I had to uncheck the "blacklist downloaded" option so that it would make sure to find at least one copy of the books, since some had been tried 3 times already.
I think it was just a hiccup for this one time, because it had worked previous as well as after this. It would seem to me that the solution would be for it to "import" the book if it is wanted even if it is not marked as snatched, similar to sonarr and radarr.
If you are running on a device that supports "Jackett", then install and run/configure Jackett. It supports a myriad of book torrents. Using Jackett as the go-between, you just point LL (via Configuration > Providers, as Torznab providers) at your Jackett added torrents per the Jackett instructions, and then for each torrent provider, also add the book categories under LL configuration 'Categories'.
1- Install and setup Jackett
2- Configure Jackett for the sources you want to use (+Add Indexer).
3- For each index added to Jackett in step 2, add it to LL (Config > Providers, as Torznab provider)
4- For each added in step 3, go to LL Config > Categories and you'll find the providers that you added. For each, add the book categories (found in the Jackett index using the wrench icon. Book categories will typically be something like (8030, 100003)...etc., depending on the specific indexer in Jackett.
Only add indexers that support books, unless you also use Jackett for other media. Good luck.