When I bought my X-T20, the package included the kit lens and 27mm. Upon inspection the 27mm had problem and I got it returned for exchange because they didn't have one in stock replace it right then. They loaned me their demo 27mm. When they couldn't fine the cap for the 27, they stuck a step down ring on it.
A couple of days later I went to China for a three months trip. A week into the trip, after using the kit without problem, I took the 27 out for a spin. Within an hour that exact error message showed up. I turned off the camera and turned on again and shooting again. Few minutes later it showed up again. I turned off and on again. And few minutes later it showed up again. I then turned it off and went home.
I was afraid that my new bought camera was faulty. And I couldn't do anything until I get back home. Still 2.5 months to go.
Well, I then hit the web and found among them the problem caused by using a filter on the 27. Sure enough, after I took out the step down ring, no more error message with the 27, or any other lenses ever since.
I guessed I was lucky that my problem with this particular error message was an easy one to fix.
I also read that some use filter on their 27 just fine. Could be that the filter thickness varience that makes the difference. Some thinner, some thicker than others.