Browser shows an error when submit handler of UI kit form takes long time

I’m trying to create an app which calls product REST APIs for multiple times in onsubmit handler of UI kit form component.
After submit, when the handler takes a long time (about 30 seconds) because of calling multiple APIs, an error like below is displayed on browser.

However, even after this error, the rest of the handler continues, and completes.

Does UI kit form perhaps have something like timeouts after submit ?
Is there any way to change the setting ?

It solved.
This may be due to total runtime limit.