I think this is happening in order to identify specific people who can be demonstrated to have some sort of link to other, unidentified instigators that the fed

I think this is happening in order to identify specific people who can be demonstrated to have some sort of link to other, unidentified instigators that the feds are after (e.g. linked via drone or bodycam or other footage showing interaction). So they pull somebody off the street in this manner, conclusively identify the person, and then pull and add that person's metadata to the Palantir graphs, in order to identify the people they can't find, or people they suspect are running the instigator show. That this is happening in Portland in particular does not surprise me at all, given the history of the city and the level of organization at protests and riots there in the past (something I have personal experience with and know a bit about). I strongly suspect that local law enforcement is fully supporting these operations, even if they are not doing so outwardly, or even denying it.