@Jonathan70
@Helen3 's explanation seems the most plausible. I've seen this mentioned before on the CC. The guest gets confused about the cancellation policy. They pay 50% upfront, but think that when the policy says they'll get a 50% refund, that means they'll get 50% back of what they paid, which is wrong. If they never paid the remainder, they are not due anything back.
You only get your payout after the check in date, so you will know a couple of days after the 26th if this has been issued or not, but it should already be showing under upcoming payments on your transaction history page.
Ask the guest what exactly they have paid and you'll be able to figure out if they paid 50% or paid in full.
If the guest paid more than 50%, then yes, something has gone wrong. If not, then it's all according to the policy. You can't get a 50% refund of the full amount if you never paid the full amount!