Can you provide more steps for rerproducing?
I think you had some kind of orphan records or broken relationships..

So the problem happens when you create a usergrp as a user and then delete the user, when you then go to the usergroups page the error is visible. The main problem is that the users dont get deleted at all from the tables "user_groups" and "user_in_groups".

Part of the problems had to do with the fact that the code assumed that if you were the owner you were in the group. In LTS it is like this, the owner is always in the group. But in master no.

Also done:

• Transfer to user 1 if the owner user is deleted
• If the owner of a group no longer exists, instead of the name it shows "(Deleted user)" in the table. (shouldn't happen, but still)
• Fixed inconsistencies in the actionViewGroup(). Things that were set inside IF statements and were always used.

https://github.com/LimeSurvey/LimeSurvey/pull/2565

My opinion : we must have a clean decision about $userGroup->owner_id == Yii::app()->user->id on the right part
We don't have this control in 3.X

I think we must have UserGroup->hasPermission with something like this

    /* superadmin can do whole */
    if(Permission::model()->hasPermission(0, 'global', 'superadmin', 'read', $iUserID)) {
        return true;
    }
    /* usercontrolSameGroupPolicy : need to be in group */
    if (App()->getConfig('usercontrolSameGroupPolicy') && !$this->hasUser($iUserID)) {
        return false;
    }
    /* Check global right only (no single rights) */
    return Permission::model()->hasPermission(0, 'global', 'usergroups', $sCRUD, $iUserID);

When decision is done about owner : we can easily add it here.

I think we must have UserGroup->hasPermission with something like this

So, you wouldn't care about who owns the group, right?

Currently no, be cause we don't care in 3.X and in current 5.X.
owner_id are not used in UserGroup permission since years … do not add it without discussion (and API update)

Then : need decision about usage of owner_id before adding it.

See the last sentence

When decision is done about owner : we can easily add it here.

owner_id are not used in UserGroup permission since years

Not sure if we are talking about the same thing... I see it is being used a lot...

https://github.com/LimeSurvey/LimeSurvey/blob/master/application/models/UserGroup.php#L191
https://github.com/LimeSurvey/LimeSurvey/blob/master/application/models/UserGroup.php#L232

https://github.com/LimeSurvey/LimeSurvey/blob/master/application/controllers/UserGroupController.php#L178
https://github.com/LimeSurvey/LimeSurvey/blob/master/application/controllers/UserGroupController.php#L190
https://github.com/LimeSurvey/LimeSurvey/blob/master/application/controllers/UserGroupController.php#L347
....

Are we talking about the same stuff?

do not add it without discussion (and API update)

No worries, I am not saying I will, I will not... Why would I?

Not sure if we are talking about the same thing... I see it is being used a lot...

Seems to didn't work with specific permission then …

Time to update to real Permission system …
https://github.com/LimeSurvey/LimeSurvey/blob/master/application/models/Traits/PermissionTrait.php

Look forward for decisions and directions ...

For LS5:
The group owner should be member of the group.
For LS6:
The group owner can be a group member, but doesn't have to be. However, the group owner should always be able to see/edit group members.