Connect database timeout by Netbeans database module

When using the database module of Netbeans to connect to the database, a connection timeout error occurred. This problem only happened occasionally on some Linux systems. I have tried it on 8.2, 11.3, and 12.3, and the results are the same. I tried to use Netbeans to develop an RCP program to connect to the database, but the problem still exists. But if you just develop a simple Swing program, there is no problem. why is that?

Thank you！