Hi @pgalamba and thanks for the detailed description of your problem!
I am quite sure that the mesh can be used for a first rough estimate and you have no illegal cells or problems with sharp corners as far as I can tell at the moment. Could you explain why you have the top inlet and outlet surfaces explicitly defined as additional boundary conditions (BCs)? I assume that these both cause the simulation to diverge due to a violation of the conservation of mass.
Unfortunately you deleted the successful runs so could have had a look at the results and see if the output quantities make sense. Tagging the @cfd_squad in any case to see if there is any impetus from their side. Once I understood why you have the top BCs I can go to the next step and see if we can make some adaptions to the setup.
Best,
Jousef