Have you left them together since they locked? How long have they been together? And they do take breaks. Mine do then I take the male out and feed him and wait a day or two then re introduce him and then it is a go again. You could try whipping sperm plugs from a different male on the females back and them putting him back in.
i got them a week ago and they have been together a few days i was planning on taking him out and feeding tomarrow as well as the female i think he trys but she slinks her tail away haha i am getting my male mojave on Wednesday so ill try that