Column dimension group isn't working

[CrashLaker]

Hi all,

im trying to group columns with openpyxl but it seems not to be working properly. can anyone help me?

ws.column_dimensions.group('M', 'X', outline_level=1)
ws.column_dimensions.group('AA', 'AL', outline_level=1)

result: it's only grouping 2 cells M-N AA-AB