This issue is already at least 2 months old, there is no one to talk with, EA truly don't care about their customers.
and if by any chance there is a developer or customer support going through the posts and actually cares (doubt it), /usermassinfo returns code 500 for over 2 months, where are your error monitors? I personally have an account with 2 consoles PC and XBOX, the PC does work, whenever I switch to xbox I am getting this error and locked out (and unable to switch back to my pc user).
this is the specific url
https://utas.mob.v5.prd.futc-ext.gcp.ea.com/ut/game/fc26/usermassinfo
server IP 35.214.117.27:443
OPTIONS works, GET fails.
update: I tried to use a VPN to US, still getting the same error 15.204.43.228:21039
update 2: for me personally after connecting to my xbox account which I rarely use and going through all the news messages pop ups, and then backing out, I managed to connect to my xbox account and to switch back to my pc user... not sure it will help you guys, but if you have 2 users too, maybe try to connect to the second user and backing out.