failure in calculating the solution

Good morning. i would like to report an issue i'm having with a non-newtonian flow and diffusion and convection system:
Specifically, when using either the variable Dof or the variable Dg it fails to provide a solution showing the following:

this happens also when i explicitly wrote the numerical value of the more complex constants. i have also tested all the variables to check for mistakes in writing them down, but they showed no such error. meaning that it should theoretically work.
the linear solver backslash in particular gives me the following errors:

Also, for reasons unknown to me, when i use other fixed diffusivities, regardless of the mesh used, it provides me negative values with the distribution shown in the following image:

and the solver backslash gives me the following errors:

As such, i would like to ask if i'm making any mistake in either defining the variables, a typo that escaped my check and tests or if it's any other issue i failed to notice and if those two issues may be related in some way.
thank you in advance
issue_non_calc_ready_to_present.fea

(Moving here for now as it is not clear it is an issue with the software, but seems more like a modeling and convergence issue.)

It is really hard to say anything with close to 60 parameters and variables. What you would need to do is significantly simplify and reduce the model (including geometry, mesh, parameters, number of physics modes etc.) to a "minimum reproducible example" where it is clear that a specific change or parameter causes an issue (for example when you change parameter "a" from "x" to "y").

good morning.
Thank you for the answer.
issue_non_calc_a_bit_more_presentable.fea

Here's the model with a minimized number of constants.
the error of non-solvability is given with the diffusivity already in the equation while the negative value in the plot shown in the previous post appear with the variable D_mol_liter.
i apologise in advance for not managing to further reduce the number of parameters.
thank you in advance.