I have just discovered this problem with my X-T20.
When I turn on the camera the eye sensor reacts properly one or two times, then it stays in EVF ONLY position.
So, this has nothing to do with cleaning the EVF or with any other wrongdoings of a user. And it is not a single occasion, as this thread proves. This is a serious problem with Fujifilm product, and Fuji should fix it without asking users to pay for repairs.
This is not the only problem my camera has developed recently. The other one is: preview button suddenly stopped working. If after taking a picture I want to see how it came out, the preview button does display nothing, no matter how many times I press it. To view the picture I have to turn of and turn on the camera, then the preview button will show the last picture taken.