Losing internet connection every night around 10:00 PM due to low signal strength

Every night around 10:00 PM signal strength on 16 channels drops, ranging from -2.8 to -5.8 dBmV, upstream drops to one channel, connection is lost, requiring a reboot of my modem to get reconnected.  During the day signal strength ranges from 2.4 to 3.4 downstream and 47.3 to 48.2 dBmV on four channels upstream with no connection issues.  The trouble is not on my end or my equipment.