I just came across this error message in 4.27.2 so thought I would relay the fix I just found… In my case it was relating to Composure output. In my output pass I has disabled “Color Conversion - Compositing Tonemap Pass” just by unchecking the “Enabled” checkbox. My output was spamming me with “This could have a slight performance impact. RenderTarget: PF_FloatRGBA MediaOutput: PF_B8G8R8A8”.
The solution was to either re-enable color conversion, or actually set the color conversion field to “None” to disable it properly.