It is maybe a general trend as my monthly bonus is around 30% lower as what I normally have. My game play is always not a lot and I only play in-house games or place some bets in the sportsbook when they offer a good promotion.
Unfortunately stake never shares how monthly calculations are taken so we don't know what we get is appropriate or not
But at least it's still fun because you get a cash bonus while us and several other users are Reload.