Hello @Edwin_Humphries and welcome to the forum!
What version are you running? There was a fix for a similar error at UNIQUE constraint failed with SIA (Support Request) [2.0.3.6], however that seemed more like a Windows problem with VSS on, and yours appears Linux. Possibly there’s a chance that the same change will have benefits in other situations. The error is basically the SQLite database saying Duplicati tried to add something already there. SQL databases often have constraints.