Hi; I would like to share an issue that happened to me today while using the ATU in 40m band. I was doing some tests in 7.290 and this is a bit off my antenna comfort zone - and I resorted to the ATU to put the radio in a comfortable operational envelope. The radio happily tunes - but when you transmit it brings the HI SWR flag. After some research, I found (not believing entirely) that this boils down to ATU board grounding pads covered with solder mask/lacquer. Guess what? It was indeed the case - and mine is a 2018 series FT-991A. I have documented the whole thing how to identify and fix in https://github.com/rfrht/FT-991A/wiki/Poor-Grounding-in-FT-991A-Tuner-Unit After fixing the grounding issue; I didn't even had to re-tune: I transmitted and got very low VSWR with the internal ATU - as expected. Hope this is of help; 73 de PY2RAF.