How old is he? Have you seen sperm plugs from this male?
If he's young....
It's possible to get some males breeding as soon as they hit 900g and under a year. Have one I raised myself who did just that...
But it's not always the case. I have one male who was very shy last year. Didn't see a single lock. Used a backup male who got the job done. This year (2years old) he's been locking without a problem.
Older.... he could just be really shy. Might need a confidence boost and a couple of visits beforehand. I suppose the other question relates to the sperm plug question...was he properly sexed? I think most breeders seem to get an unlucky improperly sexed animal at least once. I know I got one early on before I started breeding but it was sexed female, ended up male. lol