I get this error, but not the path-too-long.
If you could follow the steps in Fatal error: Detected non-empty blocksets with no associated blocks replies 3 and 6, which involve using an SQL browser (dl link provided there) and running a query, among other steps, and then posting the results it would help. Unfortunately, the file name that is messing up is not recorded. But file names “nearby” are. Might give a hint.
Interesting that your problem happened after adding a filter to exclude some files. That’s generally consistent with the theory that when Duplicati goes to remove a file, it removes it from two of its DB tables but not the 3rd.