This can be reproduced using the same steps as described in #326.

Upon import, you should see two unknown properties warnings for application.yml in start-site:

Unknown property 'spring.devtools.restart.additional_paths'	application.yml	/start-site/src/main/resources	line 1268	org.eclipse.lsp4e.diagnostic
Unknown property 'spring.resources.static_locations'	application.yml	/start-site/src/main/resources	line 1264	org.eclipse.lsp4e.diagnostic

Both warnings are incorrect as the input is valid due to Boot's relaxed binding. As you can see the properties are written using snake_case. If they are changed to use kebab-case or camelCase the warnings disappear.

There are some more details about the formats on the Spring Boot wiki.