Issues with concentration_dependent Non_newtonian flow

Good morning. I'm trying to make a model that simulates a non-Newtonian flow with concentration-dependent visosity.
The problem is that the solver keeps giving me null values.

the issue appears to be with the boundary conditions for the concentration, since deactivating the mass transport physics allows for the pure Non-Newtonian flow physics to work.
On the assumption that i cannot change the values of the variables, may i ask which is exactly the issue (i have also tried changing the boundary condition for the concentration but any non-null value gives me this issue)?
Thank you in advance
Problem_with_concentration.fea