I know I'm replying to an older message, however this might help someone in the future.
I had the same issue with my ATU-100. SWR 9.99 and EFF 33% all the time regardless of antenna etc.. I was searching for some help and came across this post.
Anyway I took my ATU-100 apart thinking of flashing new firmware and then noticed the ANT / TRX ports were mislabeled, they were reversed! All works good after correcting that issue.
