Challenge game level lowered with no explanation

[Aguaria Major]

I was under the impression that one's challenge game level is based on their level of statistic trophies, and that unless a nation falls out of the top 10% in one of those stats, their challenge level cannot fall.

Overnight, my level fell by 1 without any of my stats falling out of the top 10%.

Why did this happen?

[Ghost Land]

That's weird, though I've had seemingly random jumps or drops in level myself.

Maybe check the stats you're in the top 11-12% of and make sure none of them actually did leave the top 10% that you didn't notice?

[Aguaria Major]

That's weird, though I've had seemingly random jumps or drops in level myself.

Maybe check the stats you're in the top 11-12% of and make sure none of them actually did leave the top 10% that you didn't notice?

Done, and nothing changed to result in the lower level.