There is a regression in r54122. The last build I used last week was r53845 and it was working ok. I don't know if the regression is in any of the builds in between.
Find attached the source code of the Fedex page. I only deleted most of the address book and the profiles for privacy and left only 1st entry of those to be easy to understand the structure they use.
Created attachment 47846 [details]
Source of Fedex page
Ok, the new nightly build r54267 fixes the issue. All works as expected again.