TO DO app on Samsung Note 9 not showing notifications until inside app

Hi all,

I am a very satisfied TO DO app user, except for one crucial thing - push notifications are not working until I load/switch focus to the app.

Reminders do not remind me if:

• the phone is sleeping (screen off);
• if the phone is idle but screen on;
• if I am using some other app;

They do work when I open the app/switch focus to it. 

Tech stats:

• device: Samsung Galaxy Note 9 phone;
• Android version: 10;
• Samsung One UI version: 2.5;
• TO DO version: 2.36.178, build #178;

Any ideas on what to do? Many thanks!