I use AkeebaTicketSystem (ATS) v. 4.0.7

Under J! v.3.10.8 (and 3.10.9 as well) I get message during new ticket creation in ATS: "The application has stopped responding"

It was happened after upgrading Helix Ultimate from 2.0.6 to 2.0.8.

After enabling the "System analysis" option (Joomla! Configuration), I get an explanation:

"Akeeba Ticket System - An unhandled Exception has been detected 500 Call to undefined method Joomla\CMS\Document\HtmlDocument::getWebAssetManager() File <root>/plugins/system/helixultimate/overrides/layouts/joomla/tinymce/textarea.php Line 15"

Akeeba support suggest me: " you should report the issue to Helix since they have to update their overrides."

Can you help me?