Lovely performance otherwise, I’m really lost on why this is happening, have you an elgato PCIe card, a 2nd gpu or are you running exotic programs? Shadowplay, GForce, the list is endless, I’d even include your controllers as suspect. All I know is I’ve never seen this with my meagre set up.
As it shows up in recordings it should rule out your monitor or HDMI? cable but we can’t actually rule them out because of GSync etc. I guess it might be worth tuning up your quality settings to fly at around 60fps but keep the same balance between cpu and gpu, maybe upscale to 4k.