I've just bought three big bags of New Horizons Organic Peat Free MPC. It's FULL of wood! Every handful contains several bits of identifiable unrotted wood, and most of the rest seems to be not a lot better. There are also some shreds of plastic - both stiff and bag-type - in it. Too late to take it back as most of it's now in use but I can't help thinking it's going to be very short of nitrogen as the wood rots.
I also bought some J Arthur Bower's JI No.1, which seems excellent. But their growbags seem awful - lots of wood and plastic again.
The white stuff is probably a fungus. It's mentioned on the bag and claimed to be harmless but I wouldn't want it on seedlings.