Mushrooms are characteristic of decaying wood, and potting mix has a lot of shredded wood products in it. So this is normal.

Every national brand like that is made in various regional locations, so this bag may not be from the same place as the last bag. The composition may vary somewhat, within whatever parameters the company sets. Or maybe not always within parameters - people do goof. That may explain the chunkiness.

As far as the odor, as the weather gets hot, microbial action intensifies compared to a bag you may have bought last month. Since the bag is basically sealed, a lack of air may cause musty odors. Letting it air out should help that. Slit the bag end to end or pour it out somewhere and let sit for a couple days. Dry, sunny days.

The real test is whether plants do OK in it. Plant something and find out. Chances are it's OK.

That's good to know. I gained a lot from this.

Thanks!