I‘m sure you‘re fully aware of this old, unresolved issue. If not, please read ALL the posts in this thread
https://community.usa.canon.com/t5/Speedlite-Flashes/Canon-600EX-II-RT-drops-link-HELP/td-p/334018
There are also other threads on this topic....
It's good to hear your XPro-C works fine. It's a little confusing that between us we have 3 different controllers types and neither show the reported issue. Are we doing something wrong? I wouldn't be bothered about the 1/3 stop over exposure either...
