Having similar issue. Followed your instructions, AdMob Advertisement is now listed under Settings > Extensions.
If I open Log Viewer, and place the mouse cursor over any AdMob blocks, Log Viewer outputs "[LOG] Missing: Show AdMob %2 banner ad with Ad-Unit-ID: %0 at: %1 .help"
If I use a built in event such as the "when an ad is viewed" -placing mouse over the block, Log Viewer outputs "[LOG] Missing: event.mobile.ads.help".
What is going on?