Several.
The running surface is slatted, rather than being a single smooth belt, so that if something gets caught underneath it (more on that in a second) there's more than just friction being exerted on the trapped object; the gaps between the slats can capture skin etc.
The rear of the treadmill is open, which normally isn't a problem with a belt-driven system, but because Peloton's devices are raised off the floor, it's easy for things to get trapped and pulled under. The video the US regulators released showing a child getting pulled under happened from the rear of the treadmill, and it's a terrifying watch. Seriously, as a parent, I don't think any video has scared me that much.
There's no system to detect excessive torque / potential blockages, so when something does get pulled under the treadmill, the slats will continue to pull it further under - until either the machine gets lifted off the floor by the mass of the thing captured, or until the thing gets pushed out the other side.
Combined, these amount to a constantly-running tank track that's just high enough to grab children and pets, pull them under, and hold them there.
I want to be clear also that Peloton has a lot to answer for in terms of marketing gym-grade, dangerous devices to people who simply do not have the space to safely use them. All those design decisions are stupid and life-endangering, but they'd be less of a problem if Peloton only sold to commercial gyms. The video the regulators released showed one of these treadmills in the corner of a crowded lounge with two children playing on it. Obviously the parents are idiots for letting that happen, but Peloton's own marketing shows their hardware in people's communal living spaces - where it absolutely does not belong.