I think Tetenal recommends that you use the highest temp for consistent results. I don't have the data in front of me, but I think it's somewhere between 100 and 105 degrees F. How did you see these defects? Are they obvious to the unaided eye or did you use a magnifying glass to see them? I haven't noticed any such problems with my Tetenal C-41 kit and have enjoyed how easy it is to use. Try the higher temps and see if the problem goes away.
Best of luck and keep us posted.