Randomly (probably not) blank page displayed

Hello,

I’m quite new with Vaadin, I’m getting blank page in my application quite randomly. It happens only if I refresh it or open in new browser tab or window.
I was searching Internet trying to find the answer, but with no luck.
Vaadin version: 7.7.7
Deployment: local on Tomcat 8.0.45.
Honestly, I have no idea what information might point you at the right direction.
I have main UI class which extends UI. If user is not logged in, it sets content to login screen (it extends CssLayout), otherwise it sets MainScreen (extends HorizontalLayout).
I see in console, that LayoutManager is not processing some elements when blank page appears (console results for blank and properly displayed pages in attachement).
I’ve used @PreserveOnRefresh on UI class but it didn’t help.

Any help would be much appreciated.

Best regards
Piotr
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