Then I assume there’s a conflict with java compiler version. But did you have before upgrading XWiki the JDK 11 installed, or it’s an older version, and you’d updated it also? Please, run the command javac -version. And if the version isn’t 11, so run the following command sudo update-alternatives --config javac and choose the JVM version.
Cause from the error, we can see
- 55 = Java 11
- 52 = Java 8