Perhaps, chown permission denied.

Try www-data instead of apache.

Use cat /etc/passwd | sed 's/\:.*//' to check.

By default,

/data www-data:www-data -R 770

/elgg localuser:localuser -R 755

I strongly suggest to stick with the LTS release of elgg

As of right now, there are far more tools/plugins/themes for the LTS release than from 3.x 

Check out this post:

https://elgg.org/discussion/view/2967226/comments-and-notifications

The widgets are from ColdTrick's 'Widget Manager' and 'Group Tools' plugins. Forgot about it.

Just tested with the followed steps and all works very well:

1 - Add in start.php of your custom plugin:

elgg_register_widget_type('wall', elgg_echo('wall'), elgg_echo('wall:widget:description'), ['groups', 'profile'], false);

2 - Add 'Wall' widget on Group's profile

3 - Check on 'Show a form to add new posts' option in the widget's settings

4 - Done.

Tested on Elgg 2.3.14 / hypeWall 5.2.0 / Group Tools 9.4 / Widget Manager 8.3.2-1

@RvR, as you proposed,

ın a custom plugın,

In mod\group_tools\views\default\widgets\group_river_widget\content.php

I have added Add this:

elgg_push_context('wall');

echo elgg_view("framework/wall/container");

Before this:

echo elgg_view('page/components/list', $options);

and ıt adds the hypeWall post wıdget to Group Actıvıty wedget whıch comes with ColdTrick's Group Tools plugin.

Thanks!