Okay, so mystery solved.   I stupidly ruled out the pool as a problem, since all my other miners were able to access the same pool (litecoinpool).

I ended up doing a software reset through the GUI and then saw the L3 online and mining at antpool.   
I reconfigured my pools and it mysteriously went offline with the solid green light again.   
So, I switched to a different pool altogether (viaBTC) and it came online.   

So the solid green light appears to have something to do with the pool locking out my miners.