Exception: acados acados_ocp_solver returned status 4

Hi, I have trouble designing a tube MPC using Acados. I need to design a tube MPC for my thesis and wanted to approach this by first implementing a very rudimentary tube MPC in Acados to get a feeling how to do things in Acados.
Most errors I could fix by searching the source code to find out what happens, but the status generation cannot be found in the source code.

I got the error: Exception: acados acados_ocp_solver returned status 4

Therefore, my question is: What does status 4 even mean?

And by that note, is there some documentation what any status means? On https://docs.acados.org/python_interface/index.html, there is no explanation.

I was able to avoid the status 4 and make the system run by making the constraints more generous, i.e. giving the controller more “space”.

Thank you for your answer
Marco

Here are two relevant threads about infeasibility issues:

I suggest to look a bit more into existing posts.