Flashing red light notifies about the issues that system can handle on its own. These could be for example Internet outage or anything else that system will try again in defined number of seconds (by default 100sec). There is no need to worry about flashing red light, but if it is on for extended amount of time it is worth to check what is the actual error and try to rectify the source of it (like check the router in case of the internet outage).