You submitted the last update on December 29, 2020.
I have the latest version 5.5.3 installed but the issue is still there.
Edit:
Full error message:
REPLACE INTO `links_groups` ( `links_g_id`, `links_g_access`, `links_g_contentcount`, `links_g_dontpay` ) VALUES ( 2, true, NULL, NULL )
IPS\Db\Exception: Column 'links_g_contentcount' cannot be null (1048)
#0 /home/user/public_html/system/Db/Db.php(979): IPS\_Db->preparedQuery('/*detroitd_detr...', Array)
#1 /home/user/public_html/applications/links/sources/Members/Members.php(60): IPS\_Db->replace('links_groups', Array)
#2 /home/user/public_html/applications/links/extensions/core/GroupForm/Links.php(74): IPS\links\_Members::setGroupData(2, true, NULL, NULL)
#3 /home/user/public_html/applications/core/modules/admin/members/groups.php(224): IPS\links\extensions\core\GroupForm\_Links->save(Array, Object(IPS\Member\Group))
#4 /home/user/public_html/system/Dispatcher/Controller.php(90): IPS\core\modules\admin\members\_groups->form()
#5 /home/user/public_html/applications/core/modules/admin/members/groups.php(39): IPS\Dispatcher\_Controller->execute()
#6 /home/user/public_html/system/Dispatcher/Dispatcher.php(152): IPS\core\modules\admin\members\_groups->execute()
#7 /home/user/public_html/admin/index.php(14): IPS\_Dispatcher->run()
#8 {main}