BA is handling your claim as last airline.

They usually do not scan your bar code on worldtracer, but they enter manually the number, so that is sufficient. I remember when LHR bag system broke down last year, they had hundred of thousands of "missing" bags and it took a long time for worldtracer to have the data entered.

As you know CX and BA use different terminals at LHR, so the risk of bag misconnect is higher. Also having several airlines on the same ticket makes it a bit difficult to claim compensation as they might try to pass the bucket.

Your bag should have been delivered by now. There are six or seven BA flights LHR-TXL per day and CX255 lands early morning. If you bag just went missing for a day, I doubt that you can claim much in terms of emergency purchases. If your bag goes missing for a couple of days, then the situation will be more tricky. But both BA and CX are quite good with compensating emergency purchases. Of course, that assumes that Germany is not your home.