Well, he is used to his "routine." Granted, a switch of routines takes time.
CIO methods, is personal. For me, I didn't do that & I do not like CIO methods. Each child is different. It will not work for all. For your son, it gave him an aversion to his crib, now.
My daughter was like that. After trying ALL methods, I co-slept her to nap, and to bed at night, until she grew out of it. Once she fell asleep, I would sneak out and leave the room.
For us, the co-sleeping was on a futon on the floor of our room.
Since he is now 11 months old, you might try and give him a "lovey" of some kind to cuddle with & get attached to. AND, put some safe stuffed toys for him to play with in his crib, as "company." A crib, does not have to be all stark and bare and "empty" at this age. At this age and older, they do benefit by having at least a crib toy (ie: The Fisher Price Ocean Wonders Aquarium) which plays music and THEY can turn it on at will. My son LOVES this. By having a few safe crib toys IN the crib with them, it helps a baby/child to self-soothe them... and "entertain" them in the crib before lulling to sleep, and upon waking. For my son, he always hangs out and "plays" a little bit before falling asleep... and upon waking, he will also entertain himself...then, when he is "ready" he will "cry/yell" for me. It promotes self-direction in them, and independence.
Also, as you probably know, a distinct ROUTINE and pre-nap/pre-sleep habit is key. Doing the SAME routine, the same timing, the same thing everyday. This in time, will "trigger" in them, and sense of what is coming next... and they will know. For my son, once I start his pre-nap/pre-sleep routine, (and I do the same sequence EVERY day), and once I sing to him the SAME song before laying him down... he will automatically put his head on my shoulder and calm down... then when I finish singing the song, I put him in the crib... and turn around and shut the door. The song I've learned, "triggers" in him a reaction... to sleep. He KNOWS instantly when I sing this song, and even if he is a bit perky, it will calm him and he gets in "sleep mode."
Also, give a child time to wind-down before bed/nap....(and for me I verbally tell them that 'nap' is coming up...and we get ready) At least 1/2 hour beforehand. And, before I put my kids down for nap/sleep... I darken the room, make it a "zone of quiet" and then read or put on a 10 minute video, give him his milk, then change diaper, then pick him up, carry him in our room, turn on a fan for white noise, close the mini-blinds, sing his song to him, put him in the crib, put up the railings, then say "good-night" and then I walk out and close the door. OVER TIME... doing the SAME routine everyday will get them settled.
I know, each child is different. But it's worth a try. My eldest child, my girl, was real difficult to put to nap or sleep. NO method worked, except co-sleeping. Yes, it took stamina...
At each age, and each month, a child changes, developmentally and emotionally too, and cognitively. THIS also upsets their sleep equilibrium. AND, they also get "separation anxiety" at different ages, at different stages, and throughout childhood. So, this is something that will crop up, during different periods of their maturation and per their age stages.
Well all the best, just some thoughts. I know it's not easy and there are SOOOO many different ways a Mom tries.