hi, Sam, i was thinking you might be happier, or at least experiment, *without* =org-tempo=. so, if you customize =org-modules=, and see =org-tempo= enabled there, you might try disabling it. (to move one more chance Org is getting in the way of yasnippet.)
but, i don't know if this will help. also, the advice from Sébastien Miquel seems based on more actual knowledge. cheers, Greg