Using the LPF helps the situation but it does not correct it completely. The other meters Dave tested did not experience the same results as the Keysight meter. The "high EMI" condition, what exactly would define that? Maybe a "low EMI" condition in the right situation will cause the same behaviour?
I'm a person that just bought a Keysight u1272a meter. I paid a lot of money. Thinking it would be the instrument to help me in my Heathkit SB100 restore project. Dealing with high voltage during this project, the Keysight meter will be shut off and on the shelf.
Back to the meter everyone loves to hate. My trusty Rigol DM3068. During my little restore project, the Rigol has done the business while the Keysight meter has failed. Keep the Keysight meter away from those tubes or it will dance around.
It's not about the fancy spec sheets or chatter/excitement from people. It is a piece of equipment on your bench in your lab and it's performance and the confidence it's right. Using it with your stupid project , however big or small it is.
Sorry Keysight. I wanted to really like this line of meter, but based on my experience it's not something I want to use in my lab.
Oh well, a learning experience. Life goes on.