we used the the _timestamp fact to detect when were the facts were updated last.
the original fact name was a symbol (:_timestamp) and the new one is probably a pure string.
when storing it in the db, it no longer filter correctly accroding to the scope https://github.com/theforeman/foreman/blob/develop/app/models/fact_value.rb#L14.

we probably need to ensure its always a string, and potentially have a migration to fix older facts.