The command 'Move Down Current Line' doesn't work when the line below exists but is empty (it exists but doesn't contain a linebreak).

For example, if you have the following, with line numbers shown on the left:

1 one
2 two
3 [empty line]

If you position the caret on line 2 and try to 'Move Down Current Line', it doesn't work.

In other editors, like VS Code, if you try to move the second line down you will get what you expect:

1 one
2 [empty line]
3 two