Yeah that could be. Plenty of issues could cause it (though I am using KWin as compositor). Maybe it's fixed by now, or just a glitch on my end.

EDIT: This is weird. My monitor has different modes including sRGB. I had it in a gaming mode (higher contrast, etc...) and it shows then, but in sRGB it doesn't show.

I took screenshots and when viewing there, regardless of screen mode, it's rendering fine, so clearly it must be a monitor issue of some sort. Odd that it would render in every non-sRGB mode, but be fine in sRGB.