Latest frustration -- when I tried to load Suica from Business Gold in Apple Wallet, the charge went through and showed up on the Amex, but the Suica balance stayed the same. I made the mistake of trying this repeatedly and ran up several charges on the Amex, and am now stuck on the phone with Apple trying to get it fixed (they are still trying to figure out what happened). Ultimately after half an hour of fiddling, the answer seemed to be some sort of block accepting the payment on the Suica/JR side, which I *think* might have been because I had a VPN running at the time, but not 100% sure. Tried loading a different Suica with the same CC on the same phone with VPN off and succeeded.

Moral: if you don't see your balance update immediately after attempting a load, don't try to load again on the same card...