Frankly, he probably just isn't as polished as he was.
Dude trains a lot less than he used to and no longer is concerned with being the best. Mix that with significant stretches away from MMA, and you land here.
It's not unlike why the normally fleet-footed Gustaffson looked like crap against Bones this time around. Keeping yourself in form takes a regular schedule of training + motivation to stay at the best.
When Conor is more worried about being a celebrity and isn't taking fights and isn't training with the same intensity he used to, he's going to slip. Especially when his fights in MMA are years apart. Mix that with age (which lends itself poorly to a mobility based style, look at how Ali adjusted his style from footwork to more clinch based as he got older), and he's definitely fucked.