Yes a few users have definitely had genuine issues, most of which I believe have been resolved by Canon. There were certainly some "user errors" as well!
I found the AF on my Canon 1D4 to be excellent - that was until I used the 1DX! OOPS! That cost me some money. It is still early days with my 7D2 (the weather has been terrible over the last few months!) but it is shaping up rather better than expected in the AF department. Whilst not quite as quick and responsive as the 1DX I certainly don't feel held back by it at all.