This could be related to Jira issue KW-1974.
However, my issue happens in the DeskApp.
If you open Whatspp, switch to that tab and afterwards open a new mail (+ - Button) it sometimes happens, that you’re unable to type anything in the new mail window. However, I’ve tried it now 3 times and only one time it happened. I didn’t see any obvious difference in my 3 tries.