Kemper Stage Stereo Effects Loop Signal Coloring?

Hi everyone.

I'm running a Big Sky into the stereo effects loop of my Kemper Stage, and I'm noticing that I'm getting a comb-filtery kind of sound when I engage the effects loop (whether I have the Big Sky on or off). I'm wondering if there's something that I'm doing wrong? I'm sending from the out of the effects loop into the left channel of the Big Sky, and then going left and right out of the Big Sky into the Right and Left in of the effects loop of the Kemper. I've messed with the pre and post amp option on the Effects loop block to no noticeable change in the intensity of this sound. I looked into the Big Sky manual to see if there was some weird default setting that encourages this sound, but came up with nothing. Anyone else running stereo effects in their effects loops notice anything like this? Any help would be greatly appreciated.