Hey there, I just signed up to confirm this exact thing happening to me, too.
I run a Sapphire RX 580 Nitro+ with a Iiyama ProLite XUB2792QSU-B1 (27 inch 1440p screen, 48-70 Hz Freesync range, no LFC, connected via DisplayPort. Not the best, I know, but FreeSync should work nontheless).
I...