BADsize error on player start everywhere in level

So in game mode I can’t move anywhere. But also sometimes the player start is placed at ground level but when I press play I’m way up in the air.
There is only one small area where the player start has no BADsize error and I can move freely around in that.

The level size is Arch viz and is about 30GB. It has a light mass importance volume and a post volume.

Any ideas?

All welcome.