I thought you were completing backups previously, however if you mean you can now stop using the no-auto-compact, there would have been some extra time spent catching up on the compact.
As for figuring out which of your blocks from your troublesome dblock is the bad one, a possible method is to make a backup of the folder which has its blocks (use the previous LZMA settings), then see if you can restore all to another folder. I think Duplicati 2.0.9.x no longer defaults to the shortcut of using local blocks, so restore will likely have to read your new dblock files, and these should contain all the previous blocks that your troubled dblock has, except now each block is a small file. I think restore names files that don’t restore, and this might find the troublesome block.