Yes, I can confirm you have found a valid workaround. This should be filed as a Freesync bug with multiple monitors.
When freesync is enabled on the main or all 3 displays with refresh rate at 120Hz or higher. Video playback on all web browsers and media players will stutter. Something wrong with the frame display timing.
Issue exists in 18.7.1
Workaround: Disable Freesync on all monitors and reset PC.
Can confirm that it's most likely a Windows 10 update causing the issue, as I've had the issue appear when when I didn't even touch the drivers (automatic updates are off). Rolling back to an earlier driver that I can confirm the issue doesn't exist in didn't help either.
Can also confirm the workaround of disabling FreeSync works.
Disabling FreeSync and rebooting fixes it for me.
Just replying to say that this also resolved my issues in FFXIV. It is super disappointing that I can't use FreeSync anymore
I think for everyone seeing this, we should ensure we send problem reports directly to AMD viya https://www.amd.com/en/support/contact-email-form
Here is my rambling email I sent.
I'm experiencing the issue outlined in this AMD Community thread. https://community.amd.com/thread/230350#comment-2872516
This issue comes up if I am playing games on my main screen, have a video playing on my second screen, and have FreeSync enabled. The ultimate workaround is disabling FreeSync and rebooting. Playing in full screen mode instead of borderless windowed mode helps, but is not always a resolution.
Both of my monitors are 144hz. I generally only keep FreeSync on for my main monitor, as it supports FreeSync at 144hz. Toggling FreeSync on my second screen does not help. Reducing the frame rate on my monitors does help sometimes, but not in all games. I suspect it is a prioritization thing.
This occurred on my Fury X, and continues to occur on my Vega 64.