Why is the Shimano R3030 FD not compatible with the 3503 FC?
This is from a long time ago, but for the sake of others, I believe it's because of the cage size, I was trying to do the opposite with an r3030 crank and 3503, and I was not able to get it to shift smoothly until I paired the r3030 crank with r3030 front derailleur.