Other possibilitie: Wrong size and/or wrong thread pitch bolt used (don't use a bolt that you can't run in with your fingers), such as a metric bolt used when an SAE bolt is needed, or vice versa, bolt cross-threaded. I've seen YT videos of knuckleheads wondering why it was difficult attaching a torque converter to a Predator, using the metric bolts that came with the TC, but cranked 'em in there anyway. Bolt too long and bottomed out but bolt cranked on more. Who knows...