I should also add that I just did this same plot 5 mins ago with 3 others before this issue, and now just did another after experiencing the issue on two parts, so for some reason it is only effecting those two parts but none of the others. The only difference in the parts is the loft - It is lofted from the same inlet to different outlets
Ok I figured it out, I'll leave this discussion up though. For some reason Solidworks does not like Fillets around the inlet. It happened on both of these instances with the cut plot not working and has also made it so flow simulation doesn't recognize the fluid in earlier parts i've simulated on. Not sure why this happens but as soon as I get rid of the fillet on the inlet it works. The outlet is always Filleted and it works fine each time. Thought I'd share.