Have iOS 9 installed on iPhone and iPad. I also have Yahoo Mail accounts on both.
iPhone - Lots and lots and lots of pops up telling me my password is incorrect, try entering again. I just ignore them and Mail is pulling fine.
iPad - Would not pull Mail so I went into Mail settings and started re-entering my password for Yahoo Mail. For discussion purposes, my password contains these characters
......ica#Y......
When I enter the "Y", Settings crashes. 100% of the time.
So...any thoughts on a) why this is happening and b) why only on the iPad.