MY 50/1.4 is very old... from the EOS-5 days - mid 90's era.
Never had a focusing issue - the key there is to not stress the part of the lens that carries the glass, the part that moves in-out as it focuses. The hood on - all the time - does that, so mine still does ok.
The focusing repeatability on the 9 focus point cameras.... is so-so. At f/1.4 its hit and miss. I've tried others, and they're the same. You can set up the tests, shoot checkerboards, do all the jumping thru hoops... its hit or miss. At close distances, say under 10 feet or so, avoid shooting at less than f/2.8 if you can. Now that really sucks for me. I'm used to shooting Leica, and with my M4's or M6TTL - you focus on an eye, and the eye is in focus, assuming nobody moved. I love shallow DOF, and rarely shoot a Leica stopped down much at all.
Which leads to.... some hardware is better suited than others for certain purposes. You want to shoot close and wide open at f/1.4 or f/2.0 all the time... and have corner to corner sharp (which the Canon 50/1.4 doesn't do until about f/4.5 or so), then you choose the equipment that will do it best.
There will be an M9 in my bag very soon. Can't sell all the film Leicas, but... gotta keep one, maybe the M4-2 since I'll get the least for it.