Assuming this guy?
https://www.samsung.com/us/computing/monitors/led/samsung-27-curved-led-monitor-lc27f591fdnxza/
First point would be to confirm the monitor, so we know if it actually supports FreeSync.
The one I linked, does. But there may be others that do not.
There's a variety of reasons, and potential fixes. Remove/reinstall Crimson software would be my starting point.
There are some quirks though. For example, BenQ monitors have "blur reduction", which is not compatible with FreeSync, so needs to be off.
Not aware of anything Samsung specific, but certainly a possibility for some setting like that too.