This is a 3rd party issue.
The following change has been made in the more recent versions of Sudo:
"Added the always_query_group_plugin Defaults option to control whether groups not found in the system group database are passed to the group plugin. Previously, unknown system groups were always passed to the group plugin."
This issue has been recreated using Sudo 1.8.15.
Add the colon between the percentage symbol (%) and group name.
%:mygroup ALL=(root) /bin/sh
Add the following new option to the Sudoers file: