@SantyNet sorry I forgot to update this. In short, after running through troubleshooting with tp-link chat, I ended up having to contact the Amazon seller and exchanging the entire three pack. It was...

@B.Will The existing dimmer switch only uses two of the three wires (no neutral). There are three wires in the box though (including the neutral).

I just installed two of the three HS220 dimmer switches I bought, and for some reason the last switch I have to install is not working and I haven't seen any of the same symptoms in the forums. The...