Cura 21.03 sometimes does not display Gcode files on surface

I have been inserting “pause for filament replacement” Gcode into Gcode versions of my print objects - some after “fixing” the files with Slic3r.

The results have been unpredictable. Sometimes the loaded Gcode files appear on the Cura virtual print surface, sometimes they only partially appear and sometimes they don’t appear at all! In each case, the layer slider does appear. Also in each case, the object DOES print correctly although you don’t actually know what is being printed until it is finished…

Let me explain that last part:
I loaded two almost identical objects onto the print surface - a two-color version with the “Switch filament” gcode and a version that prints in one color. I was attempting to print two 2-color pieces by loading the 2 color item first then the plain one second. Because I could not actually see either item on the print surface, I ended up “burning” filament by making a one-color print. Apparently the two-color version “disappeared” off the print surface when the second item was loaded.

I figured while I continued refining and documenting my procedures, I would run this experience by everyone to see if anyone else has experienced this weirdness.

Thanks in advance!