Probably a silly thing which you have done but...
Did you sterilise the lids too?
Also how much of a gap did you have and how quickly did lids go on?
When I do sauces I lid asap and then leave to cool upside down so there's no cool air between the sauce and the lid. Dunno if that might help. I'm still quite a beginner. Touch wood no problems so far though.
Sounds yummy though!