A "workaround" for this is to use the hammer api & sort function provided by Unix.

1. hammer fact list --search uptime_days --per-page 250 | sort -nr -k3,3 -t"|"

The sorting is happening like it is a "word", if you remove the -n - it sorts the way foreman does. The fix for this issue would be to confirm if all the facts are a numeric number - or perhaps a more long term approach is to have a new (?) column in the database which defines what kind of search is applied to a fact.