Plesk is GUI not accessible after update from Onyx to Obsidian: ERROR: Type of GraphQL\Language\AST\ScalarTypeDefinitionNode::$kind must not be defined

Symptoms

• After the Plesk upgrade the Plesk panel is not accessible with the error:
  

  CONFIG_TEXT: ERROR: Type of GraphQL\Language\AST\ScalarTypeDefinitionNode::$kind must not be defined (as in class GraphQL\Language\AST\Node) (ScalarTypeDefinitionNode.php:5)

• After the Plesk upgrade the "Extensions" page is not accessible with the error:
  

  CONFIG_TEXT: ERROR: Type of Plesk\GraphQl\Types\SafeIntType::$name must not be defined (as in class GraphQL\Type\Definition\Type) (SafeIntType.php:0) 

• Plesk was updated from 17.8.11 to 18.0.55

Cause

This was identified as a bug with ID: EXTPLESK-4981.

Resolution

Until the bug is fixed, follow the next steps to resolve that:

1. Connect to the server via RDP

2. Execute the following command in cmd.exe:
   

   C:\> plesk bin extension --install catalog