KNIME 5.2.0 node not visible bug

Hi @JaeHwanChoi,

thanks for the report! This is very likely the same issue as was reported here: KNIME 5.2.0 - Empty Node Repository

We are working on a bugfix, making the repository loading more resilient against errors caused by loading problematic extensions.

In the meantime, you can work around the problem by uninstalling the problematic extension(s). In your particular case, you would have to uninstall some (hopefully unused) extensions and see when the repository begins to load again.
Sorry for the trouble!