Ionic tabs lang at first startup

in my Ionic 3 app I have 4 tab but I have a problem at startup of the app (real device).
When I change tab, the color doesn’t change and It seem the app have a strong lag.
The next starts of the app are ok, tab change color perfectly.
In every page I load data from Firebase Realtime Database, but the problem is not the page, but tabs.

In browser emulator I have no problem (using ionic serve).

How can i fix it?