TypeError: get_parent_class(): Argument #1 must be an object or a valid class name, string given in magento/framework/Code/Reader/ClassReader.php

I get this error when I tap “schedule new update” button in a cart price rule page

you can see in the image below, I echo $className variable, which causes the error, it displays “MexbsApBaseBlockAdminhtmlPromoQuoteActionDetailsStaging”, but there is no Staging file inside Details directory inside this module!

When I disable “Mexbs” module, everything works just fine

Thanks in advance!