Gantt select list box show / hide

When selecting the select box, the list popover is exposed and immediately closed.
Where is the part that controls the show/hide of the list pop-over?
Also, is there anyone who experiences the same phenomenon as me intermittently?

Hello Jeong,
Gantt uses a standard select element to show the dropdown in the lightbox:

There is no built-in way to change the show/hide behavior.

I tried to reproduce that issue in several browsers, but it is not reproduced:
If you can reproduce the issue in the following snippet, please, tell me the OS and browser you are using, and I will try to reproduce the issue locally:

Otherwise, please, add your configuration in the following snippet and make sure that the issue is reproduced there:
Then, click on the Share button and send me the link.
Or send me a ready demo with all the necessary Javascript and CSS files so that I can reproduce the issue locally.