Cursor or system lag may be observed on some system configurations when two or more displays are connected and one display is powered off.
This is not fixed for me and has never been fixed over the 3 years I've owned my RX 480.
I have 2 monitors. When the first monitor is off, the second stutters. The first does not stutter. The second monitor works fine in extended mode. Before, I was putting the monitors in extended mode and turning the first off, but now I run a triple monitor setup and the new monitor has displayport older than1.2.. so no hotplug and this workaround doesn't work with it.
I have tried the fix of disabling HDCP, on all monitors, it didn't work.
I have DDU'd my drivers a few times since I've been having this issue, for other issues.
I noticed that when the stuttering happened, the monitor in question would disappear for a fraction of a second from the Windows Display Settings list.
Other people have discussed this issue, for example Mouse lag or system slowdown . It seems to have a long history in this forum.