it seems that after updating to NC 18.0.6 the circles app got broken.
Users complained, that it was missing in the menu and every share using circles was missing, too.
I had a look and found the app needed an update. I installed this updates (0.18.7). After the update circles was disabled. I reanabled it.
Now it shows up in the menu, but all circles are still missing.
When opening the app, I can see all circles but clicking on an entry only stats error:
Problem beim Empfangen der Details dieses Kreises: An exception occurred while executing 'SELECT DISTINCT `c`.`unique_id`, `c`.`id`, `c`.`name`, `c`.`description`, `c`.`settings`, `c`.`type`, `contact_addressbook`, `contact_groupname`,
Problem beim Empfangen der Details dieses Kreises: An exception occurred while executing 'SELECT DISTINCT `c`.`unique_id`, `c`.`id`, `c`.`name`, `c`.`description`, `c`.`settings`, `c`.`type`, `contact_addressbook`, `contact_groupname`, `c`.`creation`, `u`.`user_id` AS `viewer_userid`, `u`.`status` AS `viewer_status`, `u`.`member_id` AS `viewer_member_id`, `u`.`level` AS `viewer_level`, `o`.`user_id` AS `owner_userid`, `o`.`status` AS `owner_status`, `o`.`level` AS `owner_level` FROM `oc_circle_circles` `c` LEFT JOIN `oc_circle_members` `u` ON (`u`.`circle_id` = `c`.`unique_id`) AND (`u`.`user_id` = ?) AND (`u`.`user_type` = ?) LEFT JOIN `oc_circle_members` `o` ON (`o`.`circle_id` = `c`.`unique_id`) AND (`o`.`level` = ?) AND (`o`.`user_type` = ?) LEFT JOIN `oc_group_user` `ncgu` ON `ncgu`.`uid` = ? LEFT JOIN `oc_circle_groups` `g` ON (`ncgu`.`gid` = `g`.`group_id`) AND (`g`.`circle_id` = ``c``.``unique_id``) WHERE (`c`.`unique_id` = ?) AND (((`c`.`type` = ?) AND (`o`.`user_id` = ?)) OR ((`c`.`type` = ?) AND ((`u`.`level` >= ?) OR (`c`.`name` = ?) OR (`c`.`unique_id` = ?) OR (`g`.`level` >= ?))) OR (`c`.`type` = ?) OR (`c`.`type` = ?))' with params ["d250a5ee-0376-1033-8f1e-d5556f8693fa", 1, 9, 1, "d250a5ee-0376-1033-8f1e-d5556f8693fa", "3989d849b84399", 1, "d250a5ee-0376-1033-8f1e-d5556f8693fa", 2, 1, "", "3989d849b84399", 1, 4, 8]:
SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'c``.``unique_id``) WHERE (`c`.`unique_id` = '3989d849b84399') AND (((`c`.`type` ' at line 1
The problem has been fixed in Circles 0.18.8 which is available in Nextcloud apps now. I had to remove and reinstall the app because the update failed. But now everything is well again.