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Thanks for asking.
Have you made those changes in Remote Buddy's Global mapping table - or elsewhere?
If you've made it in the Global mapping table:
There's a tiny timeframe between the Harmony Hub establishing a connection to the Mac and Mac apps (like Remote Buddy) being able to register to receive incoming button presses.
If the Harmony Hub sends a button press immediately after the connection has been established, that button press _may_ get lost for that reason.
If this is the problem here, one way around it would be to make sure the connection has been established, f.ex. by changing the actions in the Harmony app to look more like:
…
SAMSUNG TV - HDMI 3
MAC MINI - RED (to establish connection)
DELAY 2s (to bridge that time frame at the beginning of the connection - 0.5s should work, too)
MAC MINI - RED (now RB should definitely receive it. And if it receives it twice, it shouldn't make a difference.)
…
Hope that helps.
Cheers,
Felix