InDesign 15.0.2 on OS X 10.14.6 on a MacBook Pro with an external display.

Go into Preferences and set the story editor cursor to "block," the fattest size.

Put the cursor toward the righthand side of a longer line, and use the arrow keys to navigate the cursor up and down.

The cursor should stay visible at the end of the line, as the default cursor does.

Instead, when the cursor is at the end of the line, it disappears, making editing and navigation by arrow keys difficult.