0771, let's go into detail: where, when, whom, and under what circumstances were you not allowed to buy back? Attach a save so it's clear what we're talking about.

In my opinion, it's clear enough anyway... Additional growth of level 7, of course, can play a cruel trick:) For example, in the rules of the past World Championship, as far as I remember, they were either forbidden to buy, or you simply had to load the previous save and start the week over... But there is no such rule in the HeroesWorld rules, so you have to agree on this with your opponent right away, although this doesn't happen often..
And the best option is to play WT — there, all monster weeks and months and plague have been fixed:)