yeap, I had that as well, there is already open issue for that. Problem is with creating timer in a wait node after going though the loop. The id is the same as for the expired one and both are inside the same transaction.
A workaround for this is to make continuation of the activity (Check Order status) as async. Just add to your (assuming it is java) activity following attribute:
continue=async
And that error should go away.
Cheers,
Maciej