I have that error in Apache log, don't know if related:
[Tue Nov 26 19:46:09.322638 2019] [php7:error] [pid 2565] [client IP:61315] PHP Fatal error: Uncaught Error: Call to a member function getUserId() on null in phar:///var/www/html/include/plugins/audit.phar/class.audit.php:724\nStack trace:\n#0 phar:///var/www/html/include/plugins/audit.phar/class.audit.php(782): AuditEntry::auditEvent(12, NULL, Array)\n#1 /var/www/html/include/class.signal.php(98): AuditEntry::auditObjectEvent(NULL, Array)\n#2 /var/www/html/include/class.thread.php(199): Signal::send('object.created', NULL, Array)\n#3 /var/www/html/include/class.ticket.php(1215): Thread->addCollaborator(Object(User), Array, Array, true)\n#4 /var/www/html/include/class.ticket.php(4305): Ticket->addCollaborator(Object(User), Array, Array)\n#5 /var/www/html/include/class.mailfetch.php(890): Ticket::create(Array, Array, 'Email')\n#6 /var/www/html/include/class.mailfetch.php(939): MailFetcher->createTicket(1)\n#7 /var/www/html/include/class.mailfetch.php(1019): MailFetcher->fetchEmails()\n#8 /var/www/html/include/class.cron.php(25): MailFetcher::run()\n#9 /var/www/html/scp/autocron.php(61): Cron::MailFetcher()\n#10 { in phar:///var/www/html/include/plugins/audit.phar/class.audit.php on line 724, referer: http://domain/scp/index.php