This is a very similar problem that I have experienced. To me, it appears to just lock up. The LED is in its normal dim nature, however, any commands from any of 6 different X10 RF units do not get repeated onto the power line.
This goes for Insteon or X10 and is unpredictable. Sometimes goes for 3 or 4 days without failing. Unpluging to reset, brings it back to life.
This is a brand new unit with firmware 1.4.
Does Simplehome recommend unit replacement or are there any work arounds?