This happens e.g. on a 4:3 TV program with 16:9 commercials inserted.
Before we start ordering our new crystal ball for the year 2020, can we start by you providing us a full debug-enabled kodi.log file, so we can look at some internals? We will need more details on the what, how, and when (and why).
And which of the 7-8 RPi models is this about?