I imagine that most will be too advanced as players to benefit from this post , but this is what I have on my mind at the time. Certain key signatures seem easier to play than others. It is not that some are harder but that we are less familiar with them. Back in school my directors ALWAYS warmed the band up using Bb concert. Bb is very easy for us to play because it is more familiar. In the last few months I have taken it upon myself to remedy this problem by playing the scales that I am least familiar with first during my warm ups. I play them more often as well. I also play Clarke studies in different keys without looking at the exercises in the book while changing keys. What used to be difficult is getting easier by the day. There is no reason a person should have a harder time playing in one key signature versus another other than they have not done their homework. Even fingering issues get easier when you attack the problem combinations until they become second nature.
I plan to use this same approach with all aspects of playing going forward. I will concentrate on weak areas first until they become strengths.