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Two things:

1) do you have a context assigned to Action 2? If you do, and it is the context you are viewing, you'll see it appear after you check off Actions 2.1 and 2.2 as completed, and when you check it off, Action 3 will appear (I'm assuming you're in a Next Action or Available view mode). Note that if you are only showing one context, and Action 2 happens to have a different context, it won't appear in your view, much like what happens in the other possible case I'm about to describe.

2) do you have OmniFocus set to show projects and action groups in context mode (used to be controlled via View->[Hide|Show] Parent Items in Context mode, now a preference in the Data pane)? If you have them hidden, when you've completed Actions 2.1 and 2.2, you will not see Action 2 unless you go to Project mode, or switch to showing Remaining or All actions. You will get a report that there is at least one action available, even though none are shown, which at least gives you a clue that you need to investigate, but that's a subtle clue, and easily missed if other projects have actions in the current context.

The setting of the option in 2) above is carried around by OmniFocus sync. If you decide to do some experimentation, I'll caution that at the moment, OmniFocus does not properly recalculate the display when you change the option to show parents, so it may appear that the setting didn't get synced (or didn't do anything) unless you temporarily show Remaining actions or a different context to force it to recalculate the display.