I'm surprised as well, at least Stake treat all players equally (not only US players who received 2nd monthly bonus).
However, I lost the 2nd monthly bonus fast, I did not even able/lucky enough to increase $25 from my monthly bonus ($190).
Was up to $210 then down slowly until busted without able to make it back to $190 LOL. (played plinko and 3rd party slot with no more than $0.5 base bet).
Time to rest, waiting for the next weekly bonus to start again