can you share with as the split one transaction maybe you have only delayed transaction because this is happening sometimes most of the people few days experience of delay even not mixing bitcoin..
Much better to wait for their support to responds if what honestly the problem.. this is not a missing funds i think your problem is one of your transaction didn't arrived. can you give us the transaction you sent to the bitmixer address? so that we know what honestly the issue here .
I'm sure the transaction into the mixer went fine. I made it a point to say so in the start of the post.
It had many (6?) Confirmations when I first posted.
I doubt they would have sent half the funds without being sure the incoming transaction had cleared.
Thank you for the reply though!
PS: it did end up working out :-)