USB-C -> DP introduces horizontal scrolling lines?

[CudaMan]

Has anyone heard of this before? I can't find any info on the subject. Now that I'm hooking up triple monitors for sim racing I need to use more of the outputs on the back of my 2070. :) Problem is mine only has two DP, one HDMI, and one USB-C. HDMI is no good for high refresh rates, and it turns out this USB-C port can output like a DP port. Great. So I bought this adapter (https://www.amazon.com/StarTech-com-USB-C-DisplayPort-Adapter-Type-C/dp/B06WD4WPM9) but I see subtle yet noticeable scrolling horizontal lines on whichever screen is using the USB-C port.

I'm thinking it's the adapter itself, but before I fork out $30 on a 6' USB-C to DP cable, are there any other ideas? Cable too close to something or other?

[FaultyMario]

The "answered questions" section of the adapter says that it's not been tested in 1080p @ 240Hz, So I would think that maybe the product is not designed for higher demand applications, either that or the item is defective.

Edit: There seems to be a market niche for higher refresh-rate cables. Seems like you're going to have to take out another bill from the wallet, mister. I think they start at around 20 bucks.