IF anyone is still using this monitor I have noticed something that might help with Freesync or flashing issues. In some of the latest drivers AMD added settings that help with sub-par monitors.
Go to "Display" tab and select "Specs" on the far right of the Pixio PX277 section.
Next click on the "Override" tab and you will find yourself with two options with selectable sliders. (Adjust Voltage Swing, and Adjust PreEmphesis.)
They have adjustable parameters of 0/1/2.
According to this post https://community.amd.com/thread/212160
these options are useful for:
These options can potentially help a user overcome intermittent flashing or black screen issues that sometimes occur with monitors due to a bug or firmware issue.
This Model from Pixio definitely sounds like bad firmware. Any way I played with several combinations and the the Freesync range has improved slightly and a couple of issues I was having stopped happening. Before I played with these settings the best my monitor could do is a Freesync range of 56-144. Even then some games didn't like Freesync to be "ON" without flickering. (One of the Battlefield games comes to mind, 1 maybe)
After I played with the settings in every combination there could be, I now have a Freesync range of 52-144 and titles that behaved strangely when freesync was on, now don't have a problem.
I figured if anyone was still using these monitors this might help you out.