Same here, all is up2 date:
Notice: Undefined index: checkcontent in /home/........./modules/mod_acymailing/mod_acymailing.php on line 265
AcyMailing Enterprise : 5.10.10
PHP Built On Linux vserver272.axc.nl 3.10.0-714.10.2.lve1.4.77.el7.x86_64 #1 SMP Tue Dec 5 17:19:40 EST 2017 x86_64
Database Type mysql
Database Version 10.2.13-MariaDB
Database Collation latin1_swedish_ci
Database Connection Collation utf8mb4_general_ci
PHP Version 7.2.19
Web Server Apache/2
Joomla! Version Joomla! 3.9.11 Stable [ Amani ] 13-August-2019 15:00 GMT
Joomla! Platform Version Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
i disabled error reporting in global config. so visitors don't see the error anymore