I have a 2 year old male fire ball python that weighs in at just under 1500 grams. I have been putting him in with 5 different females ranging from 1.5kg to 3kg for 3 days at a time for over 6 months and I have never seen him lock with any of them.

I have also noticed with my other females that are being bred their vent scale is usually a little bent after being locked and I have never seen this on any of the females he was in with so I am fairly certain I am not just missing it.
My other 2 males both lock or at least start trying within hours of being put in with a female but no luck with the fire.

Before you ask it's definitely a male I have popped him there is no doubt he's male and he is producing sperm plugs.

I have tried leaving old sheds in with them, putting sheds from other snakes in with them, wiping sperm plugs from other males on the female, Introducing him right before a rain storm, introducing the females into his cage, I even accidentally put him in with another male and they went at it I guess and spilled the water bowl everywhere. they were together about 45 mins before I noticed the water bowl was spilled and realized what had happened and took him out. The other male he was put in with was a little smaller than him but he is a great breeder.
Any Ideas ?