I understand using 2 monitors via Multi-Stream Transport will split the bandwidth, so I did a calculation to make sure to have enough bandwidth.
How come I still get unequal resolution on both monitors? 

1. If you used non ATEN cables, please try with a better quality cable, or use an ATEN cable.

2. Cable length is also a factor, so please do not use a cable that exceeds 3 meters.

3. DisplayPort signal can quickly deteriorate from device to device or connection to connection, so please do not to exceed 3 connection tier.  If you need to extend with MST (Multi-Stream Transport) to more than one monitor, we recommend using the MST hub with power and built-in chipset instead of USB powered passing through hub.

4. Make sure the bandwidth used for the resolution is not above displayport 1.2.