Thanks, iituner. I have added the problem with 1D X to the listing, for the next revision.
I think that it is unlikely that Canon have changed the digital words that control these matters, as that would abandon all existing flashes. It is more likely to be the result of ever faster processors in the camera. Synchronising firing Group A and the camera reading the result, then Group B, then C is critical. The process is an outgoing instruction and synchronised, sequenced responses. Tricky.
Do Manual group levels still work? They are much simpler outgoing instructions, and I would expect them to work flawlessly.
Has this been reported to LiangGC ?
All features, including manual power control, works flawlessly
Problems only in the wireless E-TTLII with ratios in groups
I have not been in contact with Mr. LiangGC about this problem