male dog not breeding

Question
Hi, I have been breeding with great success the Bernese Mountain dog for many years. I just imported a male from Belgium, 2 years old, has all health clearances, and has had his sperm evaluated and it is excellent. One of my girls came into heat and is standing and flagging.  While he is very interested in her all he does is lick her, and not just beneath her tail but all over. He does play with her as well. She is very frustrated that he will not mount and breed her.  I have used a teaser dog to try and help things along and while he did bark and growl as well on the leash, when the teaser male was taken away he again did the same thing and never mounted. My other males says she is ready and are not hesitant to mount her, we quickly have whisked them away as soon as they mounted.  I have never encounter a male who behaved in this way.  Do you have any ideas? His thyroid is normal.

Answer
He sounds either immature to me, or as if he's had a bad experience breeding and is hesitant to try again. Under the circumstances, I'd say AI to get the breeding done and hopefully with encouragement this issue will resolve over time
good luck
Cindi