Stuck in 100%, ExceptionInInitializerError

After klicking on Play, the launcher downloads all required files and is then stuck in "100% | Done. Enjoy the server!" without starting any game.

<img width="735" height="330" alt="Image" src="https://github.com/user-attachments/assets/a147ecfc-af72-454d-ae50-41cb4b8d53f8" />

What went wrong? What could be a solution?