Wordpress instance is shown as broken
Plesk has a custom language pack with non existing locale code according to the ISO, in this case 'nl-YH'
panel.log, the next error appears:
CONFIG_TEXT: ERR [extension/wp-toolkit] Failed to get info about maintenance settings for WordPress instance #1 ('http://www.example.com'): Locale with code 'nl-YH' doesn't exists
Bug in Wordpress Toolkit #EXTWPTOOLK-3768 that will be fixed in upcoming version of the extension.
As a workaround: Set the Plesk language pack to one with existing locale code (for example nl-NL):
- Log in to Plesk
- Tools&Settings > Languages
- Select one standard language (for example en-US)
- Click on Make Default