I have the same problem with my Philips 349x7fjew. This is a bad implementation of freesync. Now I understand why it's best to spend more on Gsync but have everything that works.
Not true. I am seeing a bunch of posts about flicker present even on Gsync monitors
That happens with VSync, FreeSync and G-Sync for some people...
Same problem with the BenQ XL2730Z, connectet with DisplayPort...
My PC Specs:
AMD Ryzen 7 1700 3.00 Ghz (3.70 Ghz)
AMD RX Vega 56 8GB
Gigabyte Aorus GA-AX370-Gaming 5
16GB DDR4 Ram
2560x1440@144Hz 27' Monitor
Windows 10 Home (Fall Creators Update)