Hi there,
When dealing with simulations at very low Reynolds numbers where the flow is predominantly laminar and linear, there are specific adjustments and considerations you might want to make in your simulation settings to optimize convergence and accuracy.
You are right, the convergence settings (under-relaxation factors etc) have to be adjusted accordingly. Also, it is important to have a look at the mesh, the solver settings and the numerics (along with the tolerances).
Can you please share your project? It might be helpful to have a look 