Hey, I’ve checked with the team and this is because you have an active explore run in the Underspire Kingdom and that was while there was a mythstone bonus there.
It was decided that rather than resetting your mythstone bonus for the Underspire Kingdom when you’re potentially 3/4 of the way through a level 12 explore run, we would allow the bonus to stay there so you don’t miss out on the rewards you were expecting to get.
But because it’s changed to an Underspire Kingdom, the mythstone bonus icon disappears from the Kingdom so it’s nbot begging to be clicked only for you to find it’s the underspire kingdom every time you open it as that would be frustrating.
If you don’t have an active explore run with mythstone bonus in the Kingdom when it ticks over to the Kingdom’s Underspire week, then you will continue receiving 4 mythstone bonus kingdoms throughout the week as it won’t trigger there on the Underspire Kingdom.