Rebuilding contacts is the useful half; the balance decides whether zaps change at all. Minibits keeps two balances apart, and the ecash sitting in the mint is not the Lightning balance you can spend. So a contact holding only a Lightning address still cannot zap what is only ecash. Add iOS suspending the app in the background, and a zap can sit until you reopen it. Saving plain Lightning addresses as contacts helps most for the people already on the Lightning side.