PyQt5 - Dialog pops up immediately on opening for the first time, but far slower on subsequent uses.

[KASULA]

This post is deleted!

[JonB]

@KASULA
Not really: get rid of all this "thread handling" stuff, and saving data etc., and see how the dialog behaves.

Since you (seem to) intend to create a brand new dialog each time, try setting the Qt.WA_DeleteOnClose flag/attribute on the dialog, does that make any difference?

def return_cancel(self,new_form):
    new_form().reject()

Do you press Cancel in your timings? Because this code is wrong.