Popup View float down when trigger keyboard

[mrkhanhkhi]

Hi guys,
I'm currently facing a problem as below:
Step 1: I'm using a popup view for login form, when I touched the textfield, the keyboard popup and pushed the popup view upward normally.

Step 2: But when I lock the device and reopen it, the popup view slide down and comeback to the old position, this animated quite fast in one second.

Step 3: Dismiss the keyboard and the popup view slide down to the bottom of the screen.
According to my observation, it seems like the popup was reinit when i open the device again. Because when i close the popup, the background view still remain.

Here i would attach the image:
https://imgur.com/UgJS6zn

Thank you so much !
P/s: Seems it only appear in Landscape mode, i tested on iPad mini, ios 12.2