Just FYI. While upgrading an installation I think I was faced with the same situation.
The output looks very similar. There where some refactoring efforts in this part of Redmine and a function/method which is used by the redmine_agile plugin has been renamed.
Open app/models/agile_query.rb in the redmine_agile plugin folder. Look for the function groupable_columns and replace the function call c.groupable with c.groupable? and that's it.
Afterwards the function should look like this.
defgroupable_columnsavailable_columns.select{|c|c.groupable?&&!c.is_a?(QueryCustomFieldColumn)}endI hope I could help you.
Kind regards,
Bernhard