It's a bit of an edge case with AMS which only happens in a 5+ party set up if one of the parties is polling 45%+ of the constituency vote and everyone else is sharing the other half of vote evenly-ish.

Which is accidentally the situation we find ourselves in Scotland.

I'm not sure it's soluble by adjusting the allocation of seats between constituency and regional list. Shifting from d'Hondt to the Sainte-Langue method might reduce the gamability. Not sure.

AV+ probably does fix the problem in practice. Difficult to implement that under the circumstances.