My guess (on a thread you were on) is below. Would you consider donating some hours to explore this? Basically, it’s a whole lot of clicking plus record-keeping. Retroactive testing is probably too much to ask. Previous note here also points out that there is no downgrade test suite, so precision data loses value…
Error accessing database version 9 plus a note that 2.0.4.5 does 8, and I’m not sure I want to go further, however I suspect the table at top could use confirmation, and there are also two different DBs involved.
I’m thinking v2.0.4.13-2.0.4.13_canary_2019-01-29 through (so far) v2.0.4.22-2.0.4.22_canary_2019-06-30 however if you’re not testing bleeding-edge canary releases, v2.0.4.21-2.0.4.21_experimental_2019-06-28 might be what you had.
Basically, to be the most helpful, one would say where a DB got added on each of the release channels. Databases for the server DB and the backup DB go independently, but either one can hurt a downgrade.
https://github.com/duplicati/duplicati/tree/master/Duplicati/Server/Database
https://github.com/duplicati/duplicati/tree/master/Duplicati/Library/Main/Database