I've been staring at this for quite a while, thinking that surely 'partition_group' is spelled wrong in one of the two places, but it's not. I've tried a number of changes to the query, deactivating / building / reactivating partitioning, etc. No matter what I do this error persists. The name, the type, and the position of the partition are all as they should be. The error message is telling me that I MUST do precisely what it's telling me I did do.
This is from sqlexecutor within a Python recipe, but the same error occurs if I try to use a SQL query directly.
It turns out that if I move the partition column to be first, the problem goes away. I'm still not sure why this makes the problem go away, but it did (yes, it is best practice so that any changes to the other columns don't change the position of the partition column but this particular instance was an exception).