Triple Crown achievement not unlocking

Has anybody else had problems with the “Forza Triple Crown” achievement not unlocking?
Mine is showing as being stuck at 66% despite having all 3 of the required achievements unlocked.
I unlocked them in the following order; First Time, Street Legal, and then One Down.
Have hard reset the box and re-raced them all but its still not unlocking.

Update
Its finally showing as unlocked and my gamerscore has increased, but it did not “pop” like a normal achievement so i guess the servers may have just been slow to pickup the completion criteria being met.