Hi!
Using shotwell 0.26.3, this is what I did:
1. I `apt purge shotwell`, so it should reset all my configs and ddbb.
2. I installed shotwell again. Unexpectedly, shotwell kept the config I had in "Preferences": Library Location, Directory structure, External Editors, as well as I think the plugins I had enabled.
3. When launching shotwell, it starts to re-build the database corresponding to the Photos Library as I would expect.