The post covers that, though not by that name:

And even more problematic, some of the algorithms will run forever without producing output—and we can't prove they will never stop running. This is known as the halting problem, and it is a deep fact of the theory of computation.

When Solomonoff induction runs into a halting problem it may well run forever. This is a part of why it's uncomputable. Uncomputable is a pretty good synonym for unprovable, in this case.