skatercorpse

Found the fix/solution for me:
In order to work properly (on the X-T50) the option "Interlock MF assist & Focus ring" has to be OFF. 
I don't think it makes sense....but it is what it is 😅

Hi folks,
I got an official reply about the "Interlock MF assist & Focus ring" option with MF lenses.
Don’t fret, what you’re experiencing is normal. The question that would showcase why it’s not working would be:
“How would the camera know when the focus ring is moved without a way of communicating that to the camera body if there are no contacts on the lens to pass that information?”
Essentially with FUJIFILM lenses (and basically almost all new lenses from every manufacturer), moving the focus ring changes focus electronically so the camera knows when the ring is moved through software/hardware, without that, like with vintage lenses with mechanical focus, there isn’t a way for the camera to electronically know when the ring is moved, so the function won’t work as intended to turn off/on MF assist when the focus ring is engaged.

Exaclty, I also read it and I got it how it should work. It doesn't make sense to me that it doesn't work with MF lenses. But I've just tested another MF lens (so three in total) and same behavior. 
Works correctly with AF lenses.

Would be great if someone else could test the option "Interlock MF assist & Focus ring" on the X-T50 with a manual lens in order to understand if it is correct it only works with AF lenses or if my camera has a bug

Kind of hope so, that would mean they might fix it...sooner or later