No such file or directory – suddenly, with basic installation

When calling Home URL, in this case a subfolder like http://domain.de/upicrm this comes up:

Warning: require_once(/home/www/domain.de/upicrm/wp-content/plugins/upi-crm-universal-crm-solution/classes/upicrm_webservice.php): failed to open stream: No such file or directory in /home/www/pekic.de/upicrm/wp-content/plugins/upi-crm-universal-crm-solution/upicrm.php on line 86

Fatal error: require_once(): Failed opening required '/home/www/domin.de/upicrm/wp-content/plugins/upi-crm-universal-crm-solution/classes/upicrm_webservice.php' (include_path='.:/usr/share/php') in /home/www/domain.de/upicrm/wp-content/plugins/upi-crm-universal-crm-solution/upicrm.php on line 86

Line 86 has this in it:

require_once( plugin_dir_path( __FILE__ ) . 'classes/upicrm_webservice.php' );

Only plugins running are UpiCRM and Automatic Plugin Updater (1.0.2).

When renaming plugins folder, backend shows, when logging in by /wp-admin.

When renaming again to standard name same error apperas again.

When deleting UpiCRM from plugins dir (by FTP) backend shows.

Updating to WordPress 4.6 now and reinstalling UpiCRM (2.1.3.0).

Works again.

https://wordpress.org/plugins/upi-crm-universal-crm-solution/