Search API - people - person.folder - An unknown error occurred

When i try to use the search API to search for people and filter on person.folder i always receive the error "an known error occurred". several other filters using the same search API to find people work just fine.

is there an issue with filtering on person.folder or do i need to adjust my filters somehow so it does not produce the error?

i am using curl to run the command and my filter looks like this:

{"filters": [{"name": "person.folder", "value": ["Cand:Unreviewed"], "operator": "=" }]}