Axial turbine stage Fluent setup
 

Hi all,
I am working on a simulation of one stage of a high pressure axial turbine as can be seen on the first picture. My domain consists of 2 stator blades and 1 rotor blade. Rotor blade and rotor hub are rotating around Y-axis and the rest of the walls is stationary. Between stator and rotor I use mixing plane and run this as steady simulation. Pressures are defined at stator inlet and rotor outlet.
I tried many different setups regarding segregated or coupled solver, turbulence models and discreatization methods but every time I seem to end up with the same and wrong flow field. As my rotating speed of rotor blade and hub is quite large (almost 1000 rad/s) quite often simulation crashes on the very beginning so I tried also gradually increasing the rotation speed. At the beginning, the flow field looks reasonable as shown on the second picture but as simulation continues residuals actually converge but I get completely wrong flow field as shown on the third picture. This then causes funny velocities on mixing plane where on stator side it looks ok but suddenly increases on the rotor side (fourth picture - shows mixing plane - overlapping of stator exit and rotor inlet) (?).
Did someone tried simulating the whole stage of axial turbine or compressor and might know where could be the problem? I appreciate every help.

Thanks :)

https://imgur.com/rOsa1KK
https://imgur.com/KQPeYLG
https://imgur.com/xIzQ1OQ
https://imgur.com/8yhn1ic