Unfortunately, after numerous tests 1DX with YN-622C revealed the following:
In most cases, E-TTLII is not working properly (the unpredictable spread of flash power level). Sometimes, in very rare cases, the wireless mode is turned off E-TTLII working correctly.
So I deleted 1DX from the list fully compatible cameras on my website WWW.YN622.RU
Excellent work only manual power control and all other functions.
YN-622C always controls the flash installed in the transciever hot shoe.
Therefore, errors in the T-TTLII will even put the flash in hot shoe YN-622C on the camera.
If you only have one flash on the camera needs to be E-TTLII, then perhaps it is best to use a simple trigger with the pass of TTL, for example COMMLITE Commtrig G430 or Phottix Strato II.
I will remove my post above about compatibility.