Mine has always given problems. Mostly, like
@Fearless Tower example, there's an expectation that the last two characters be letters, but then yours has a number. In my case with 10P, when pronounced with nominal quickness inflight, it's phonetically hard to distinguish from the all too common "SP", as found in re-start production Cessnas. So unless I make a point to pronounce it sllooooooowly as in , bla bla One-zeROOOOOOOWWWW....PAPA! it just gets read back Sierra-Papa. It's a PITA. Additionally, since comanche tail numbers tend to end in Papa as well, I get called a comanche as well too, though that one is inconsequential to me.
Of course, I could always go the overnugget/carrier-break dooshbag RV-driver route and just use a tactical callsign.