Originally Posted by The Wizard:
“I did but I halved it so only used 250g icing sugar and I used 5 egg whites as I only had medium eggs not large. Same result. I don't think it's the mix that's the issue I think it's the cooking.”

There could be fat residue in your bowl, egg shell, tiniest bit of egg yolk. These can be reasons for it to collapse and ooze during the baking.

For a dry meringue often boiling sugar will be used, hence why I said to beat over a hot water bath.