They may read like so many others, but what I don't understand is why special agents in the FBI would take it upon themselves to report strange phenomena.

This seems like it would be a CLM, as the authority of their testimony is central to their function as federal LE.

For example, see this document: https://www.war.gov/medialink/ufo/release_1/western_us_event...

(from series of documents from incident data 9/1/23)