If your popup is created by JavaScript, the following topic might help you.
In that case, the activity for showing the dialog (not the click activity for button) is waiting response from JavaScript. Setting HardwwareEvent in the first Click activity solves this matter.
But I still would like to know what is causing the issue.
Unsure if it is the activity before or after the popup is waiting on some kind of completion?
But the UiPath REF I feel should still handle it as a SE with the default 30 sec timeout, but im maybe wrong.
From this, can you try SingleWindow at WindowAttachMode of UseApplicationBrowser activity because SingleWindow mode is similar with classic Attach/Open Browser activity?
I have tried this now without any success. UseApplicationBrowser/NApplicationCard was modified before and after where the popup window would appear. Also tried with Hardware events and chromium API, no success.