This could be a couple things. So i’ll try to make a recommendation for each.[br]
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1. Check your cables. If you are using something with a 4k output to a 4k monitor but not using 4k cables then I have seen some strange display issues. If it is an older cable try a newer or different one just to rule out that it isn’t that.
2. Check another device. Does the monitor still have the same issue when something else other than what you are currently using is hooked up?
3. It’s the monitor. It could be either the main board or the panel itself. Normally if it is a panel though you would see the lines at all times.
I hope this helps a little!