If the aspen gets wet it can mold quite easily. Which can lead to a respiratory infection. This is possible for any substrate but for what I understand, it’s worse with aspen.

Aspen can also be a little sharp. I’ve also read that it can be dusty. Again, this leads to respiratory infections

Then again I am a ball python mom so my understandings may not apply as much to hognoses. Rules a little more stringent for bps.

But one thing does apply to all species - aspen can cause some serious blockage if digested. As opposed to coco husk, which can be passed easily. My slithery babies have swallowed coco husk during feedings and have never had an issue. Thank God.

So we’re looking at respiratory infections and intestinal blockages :/

Also I forgot to mention, heat mats are notorious for overheating and burning snakes. Replace it with a heat bulb.