MS To-Do app stops responding when on the 2d screen and being idle (not in focus) even a few seconds

In my case, there's laptop and an external monitor connected to it. MS To-Do app is always opened only in the external display. It's always in full screen.

When I interact with the app (e.g., add a new task or adding info into an already created task), then switch to another app (e.g. Google Chrome on my main laptop's display) and then return back to the To-Do app, it stops responding COMPLETELY. Wherever I click on the app, it just won't react at all. The only way to bring in back to life is to kill it and relaunch again.

But repeating this "kill-restart" cycle 50+ times EVERY SINGLE DAY is madness! 

Please fix this super-frustrating behaviour of the app ASAP!