I think you have a flawed supposition: "The reason being that it is difficult to conceive a computer, alien or otherwise, creating a universe in which there are problems which it itself cannot solve."
...Unless the alien is creating the simulation for the purpose of solving equations they cannot otherwise solve. We do this now with computers (AI and DL being examples).
Perhaps you're right, and as you point out we do this with computers now. However the difference is these computers do not hold a complexity that is near infinite. Which is what it would require to create a simulation that included consciousness and quantum mechanics.
In my humble opinion, the thought of a computer that can work out each position of each atom in such a vast space in realtime, yet not be able to solve equations that were generated by its own generations, is not a plausible one.
Cryptogee