yes , loads of people on here having the same issue with the heat pump dryers . Yes its design / technical reason is not reverse tumbling throughout the whole drying process.
Saying that , even conventional (vented and condenser) tumble dryers with auto reverse throughout the tumble can bunch up sheets into a large ball too.
You could try tossing in 2 or 3 tumble drier balls and see if that helps the issue .
