Frank Mir had a lot of rough knockout losses. Interestingly, his fights with Arlovski and Overeem both glass cannons themselves both went to decision.
Arlovski might be the worst culprit among accomplished top level fighters. It wasn't as if his poor whiskers got exposed midway through his career, he was KTFO in his very first mma fight. Overeem also has a legendarily weak mandible.
How about Marvin Eastman, who was kayoed by a glancing JAB by Travis Lutter, who didn't have any other notable knockouts that I can recall. Word on the street is that he was kayoed either once or multiple times in training before the fight and didn't have a chance to let his head recover. Forrest Griffin is as resilient as they come, with a huge heart, but he had his lights shut off a few times against Anderson, Shogun, Keith Jardine, and Rashad. Wanderlei Silva had some awfully embarrassing quick kayo losses against Vitor and Chris Leben, but that might be balanced out by surviving Mark Hunt's bombs in that fight.
