I am not sure the validity of this claim from Wikipedia on 't Hooft–Polyakov_monopole
The "monopole problem" refers to the cosmological implications of grand unification theories (GUT). Since monopoles are generically produced in GUT during the cooling of the universe, and since they are expected to be quite massive, their existence threatens to overclose it [clarification needed]. This is considered a "problem" within the standard Big Bang theory. Cosmic inflation remedies the situation by diluting any primordial abundance of magnetic monopoles.
If monopoles are massive, we may not detect monopoles -- I do not know what does it mean to say "their existence threatens to overclose it"? If we cannot detect monopoles due to monopoles are massive, then why there is a "monopole problem"? It may be that we can find monopoles only if we can reach the GUT scale?
"the standard Big Bang theory. Cosmic inflation remedies the situation by diluting any primordial abundance of magnetic monopoles." What are the differences of standard Big Bang theory versus Cosmic inflation? Do the remedies of the two the same idea or no?