the group_admin relationship is not something from core. Group Tools adds the relationship. It also takes care of the extra rights via access related hooks. Maybe your copywork contains the creation of the relationship, but does not provide the extra access/rights that this role should give group admins.
Thank you for your reply. You are absolutely right. If the group_admin relationship is not from core, then I must have missed the 'extra access/rights' part. I tried to find these related hooks as you suggested, but only find these lines of code in start.php:
elgg_register_plugin_hook_handler('default', 'access', '\ColdTrick\GroupTools\Access::setGroupDefaultAccess'); elgg_register_plugin_hook_handler('default', 'access', '\ColdTrick\GroupTools\Access::validateGroupDefaultAccess', 999999); elgg_register_plugin_hook_handler('access:collections:write', 'user', '\ColdTrick\GroupTools\Access::defaultAccessOptions');
but none of them seems to be related to the group_admin's rights. Do you mind telling me what hooks should I look at regarding the extra rights of group_admin? Thanks.
found it. It's this permissions_check hook handler:
elgg_register_plugin_hook_handler('permissions_check', 'group', 'permissions_check');