Not receiving notification of "order processed"

In orders > order statuses > processed I have “notify orders department” ticked, but don’t receive an email.

If I manually save an order with “notify orders department” ticked it does send an email to the orders department address, so that can’t be the problem.

Any ideas?

I’m sure the answer is obvious but felt I need to ask: Is the order in question in the Processed status?

After setting this, have you cleared your cache?

Yes, definitely in the processed state. I will try clearing the cache to see if that helps.