WP_Ajax_Upgrader_Skin not found

When tried to install plugin from the WPMUDEV Dashboared it is showing Server error status: error [500] at the top and the error log is showing something like

PHP Fatal error: Class 'WP_Ajax_Upgrader_Skin' not found in /xxxxx/wp-content/plugins/wpmudev-updates/includes/class-wpmudev-dashboard-upgrader.php

I have found this https://premium.wpmudev.org/forums/topic/php-fatal-error-class-wp_ajax_upgrader_skin
I was using the 4.9.5 and after updating to 4.9.6 it worked for me. I am would like the developers to check the issue and understand the problem and build an error message for it