Please upgrade to iOS-2021.12.1 and core-2021.12.6, which includes fixes that work in tandem to hopefully address the problem. core-2021.12.4 and core-2021.12.5 had a bug which caused the page to blank out when the workaround was attempted.
I have been seeing this issue since atleast the initial 2020 Home Assistant iOS app release… Whether it was caused by that update or a Home Assistant update - I have no clue
I am also affected and this is quite annoying. Many times when I open the iOS app after it was in the background for a while, it lags dramatically, so input (cliks, swipes, etc.) are just considered with multiple seconds delay, before the screen ist just frozen. Sometimes it gets better afterwards or also with a manual refesh, sometimes it remains less responsive than usual.
Quickly killing the app and restarting it solves the issues, then the interface is as fluent as expected.