Control the GroupBy node via variables fails --> Bug(?)

Hello,

I’m trying to control the GroupBy node via variables. To do this, I create a list of columns and a list using the aggregation method. Nothing special.

GroupBy config:

Unfortunately it does not work. I get an “out of bound” error:

I am using KNIME 5.2.1

When I reduce the number of columns to one (still a list type), it works, but with multiple columns (see pics above ) not.

(Yes, I checked the other topics of this forum, but no solution found.)

Thank you in advance.