We had this error with our custom plugin. Here is our internal report of the bug and the "fix"
Plesk WordPress Toolkit - Plugin Version Validation Bug Report
Summary
Plesk WordPress Toolkit incorrectly rejects valid WordPress plugins with the error "The underscore character is not allowed in...
I manage multiple plesk servers for multiple clients and this is the first time I have come across this one.
The client changed the username in the "System user's credentials" section of the hosting settings.
This then broke the php-fpm on restart with this error message.
Error: phpinimng...
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