Please fix PHP issues the following way on the Plesk Control Panel system:

1) Login to the new panel, go to the specific domain and click PHP Settings.
2) Set PHP & FastCGI settings like the following on the PHP Settings page. If the values are not editable let us know to make them editable for you.

PHP Settings:

256M (Default)
max_execution_time: 600
max_input_time: 600
post_max_size: 64M
upload_max_filesize 32M

* The dropdown boxes are editable.

Enable FastCGI settings:

maxInstances: 0 (Default)
activityTimeout: 600
requestTimeout: 600
instanceMaxRequests: 200
queueLength: 1000
rapidFailsPerMinute: 10

3) Set the permissions the following way using the File Manager in the new Control Panel. If the main domain you will set the permissions on the HTTPDOCS folder. If a secondary domain, you need to set the permissions on the folder with the same name as the domain.

A) Go to the top level (Home Directory) and click the three lines icon on the far right of that particular folder and select "Change Permissions".
B) Click on the Application pool Group and give Full Permissions
C) Tick the box "Replace permission entries on all child objects with the entries displayed here".
D) Click apply. It may take a few minutes.