Plesk is GUI not accessible after update from Onyx to Obsidian: ERROR: Type of GraphQLLanguageASTScalarTypeDefinitionNode::$kind must not be defined

Symptoms

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

  ERROR: Type of GraphQLLanguageASTScalarTypeDefinitionNode::$kind must not be defined (as in class GraphQLLanguageASTNode) (ScalarTypeDefinitionNode.php:5)

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

  ERROR: Type of PleskGraphQlTypesSafeIntType::$name must not be defined (as in class GraphQLTypeDefinitionType) (SafeIntType.php:0) 

• Plesk was updated from 17.8.11 to 18.0.55

Cause

The upgrade 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