3-way switch not turning off light
 

I have a duplex switch (that I just replaced) with a 3-way on one side and a single on the other. For some reason, since the replacement the 3 way isn't turning off. Is it more likely that the Commun (hot) is on the wrong side?

Looking for a good answer before I keep trying new wiring patterns.

I'm not sure what you did based on your post but, a 3-way switch only work in conjunction with another 3-way switch on the same circuit.
If this was already a 3-way and it's not working after replacement, you either have a bad switch (test it with a volt/ohm meter) or you miswired the switch. If you think you miswired, pull the opposing switch and this will tell you which wire is your traveler wire(common hot).