Cannot duplicate/copy protected content

[bailiwick]

CMSMS 2.2.8

Unable to use the content manager's 'copy this page' icon to dupe an existing, protected content page.

Generates an error:

AH01071: Got error 'PHP message: PHP Fatal error: CMSModule::main(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "FrontEndUsers\\ProtectedPage" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide an autoloader to load the class definition in /var/www/vhosts/mydomain.com/httpdocs/modules/CMSContentManager/action.admin_editcontent.php on line 84\n', referer: https://mydomain.com/

Any ideas?

[DIGI3]

Worked fine for me in 2.2.15, FEU 2.14.3.4, and PHP 7.2, so you may need to provide more specifics of your versions of FEU and PHP, and test in the latest CMSMS release.