Being able to start a reliever on 2 days rest is not a bug. If they have the appropriate amoung of BFA thats how the game is supposed to work.

Being able to start ANYONE two consecutive games IS a bug which is due to some combination of
(1) BFA not being computed correctly
(2) Game not degrading pitchers enough who are not ready

I assume that (1) is a database/server problem. And (2) might be a game problem which hopefully (please?) will be resolved in the new version of the game which they say will be out by the time the playoffs start in founders leagues (which is about 5-6 weeks from now)