Were you using any home appliance or power tool when the charging was interrupted? I have a CC LCS-20P EVSE and while I don't use delayed charging I found that whenever I use my Sears Craftsman plug in leaf blower the EVSE shows a power error due to a ground fault. It does not matter which power outlet I use, the CC EVSE always indicates a ground fault error when I use the blower. I contacted CC, I was able to speak with an engineer who explained that the CC EVSE is sensitive to noise on the ground wire, evidently the leaf blower motor was especially noisy. The engineer explained that the CC EVSE is designed to reset automatically following a power fault after approximately 17 minutes so this may explain why your HCS-40P did not immediately clear the fault condition but later on you could resume charging. I usually charge my Volt at night, not during a time when I use the leaf blower, so this does not interrupt charging.