CAX80 partial WAN accessibility cut-out at 18:01 MT every night; again in early AM

Equipment: Netgear CAX80 modem/router. Hardware version 1.01, Firmware version V2.1.5.2; Cable Firmware Version V1.02.08. The modem is provisioned by Comcast/xFinity. 

Problem:

• Since early to mid-June my WAN accessibility partially cuts-out at 18:01 MT every night. You can set your watch by it.
• When WAN access fails the Internet Access traffic light goes red. The Upstream and Downstream status lights remain green. 
• The cut-out is only partial: the xfinity web site is accessible, and generally (but not always) google is accessible. Sometimes a few other web sites (e.g., local community newspaper) remain accessible; however, almost all others - including biggies (nytimes.com, washingtonpost.com) - time-out.  
• I use imap for my mail: generally gmail is received, but cannot be sent (smtp server not available for outgoing mail); iCloud mail is not received and cannot be sent and the iCloud web site is inaccessible; the MS-Exchange server from work is inaccessible; and, connectivity to other mail services is also cut-out. The Comcast mail server appears to work fine. 
• To be clear, this behavior is identical for both wired and wireless devices accessing the internet via the CAX80. 
• At least some neighbors have reported similar problems. 
• A similar cut-out takes place sometime in the early AM. I've not stayed-up all night to see if it is also takes place at a regular time. 
• I've been round and round (and round) with xfinity service, which has not been helpful. 
• In mid-July I manually switched my router away from xfinity's DNS servers to use google's. There was a slight change in symptoms: the 18:01 cut-out still occurs, as does the early AM cut-out, but with a modem reboot immediately after the 18:01 cut-out I am generally able to recover full connectivity. Similarly for the early AM cut-out. Previous to the DNS change I was unable to recover WAN connectivity, with or without a modem reboot, until morning (generally between 8:00 - 9:00) when a modem reboot would recover WAN connectivity. 
• Modem diagnostics consistently show good upstream and downstream signal power and SNR (32 downstream channels locked with SNRs between 39.9 and 40.4 dB; 6 upstream channels locked with power between 36.3 and 42.3 dBmV). The modem event log shows many "No Ranging Response received" and "SYNC Timing Synchronization failure" messages during the outages. 

For completeness I've attached the (current) cable diagnostic log. 

Thoughts? Ideas? Magic incantations?