Random DB Error

I've been having several of this entries on Roundcube's log, calendar tasks seem to be working correctly, but this is being logged:

[13-Apr-2019 08:05:30 -0300]: <b1g58bpm> DB Error: [1064] You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')
       AND e.uid='465811622A9DDB72B4054E86F529-24D1AC3C6011C35A'' at line 4 (SQL Query: SELECT e.*, (SELECT COUNT(attachment_id) FROM attachments
         WHERE event_id = e.event_id OR event_id = e.recurrence_id) AS _attachments
       FROM events AS e
       WHERE e.calendar_id IN ()
       AND e.uid='465811622A9DDB72B4054E86F529-24D1AC3C6011C35A') in /home/********/program/lib/Roundcube/rcube_db.php on line 543 (POST /?_task=calendar&_framed=1&_action=itip-status)
[13-Apr-2019 08:05:30 -0300]: <b1g58bpm> DB Error: [1064] You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')