"Invalid IP Packet" displayed in logs constantly and passthrough router has problems

For several weeks, my home router (Netgear R7000) has been crashing multiple times a day.  It starts dropping connections to devices and becomes completely unresponsive.  I have to power cycle it to get it working again for several more hours before the next crash.  Finally, Netgear released a firmware update, which I installed.  The all-out crashes stopped, but now the router's connection to the internet through the AT&T Arris BGW210-700 will "hiccup" a few times a day--by this I mean that the connection will drop for about 10 seconds.  If you are streaming something or otherwise doing something that requires a consistent connection, it will drop and then restore after 10-30 seconds, but I don't have to power cycle it anymore.  

I was convinced the issue was my router, but I now think it may be a setting on the AT&T modem.  The logs in my router, which I previously could not get to when it locked up because they got cleared out, show "Internet disconnected" and then "Internet connected" about 1 second apart, which is when those network hiccups occur.  Viewing the Arris modem logs, every day there are hundreds of entries showing "Invalid IP Packet" entries that show my network as the source and any series of destinations that don't seem to have a pattern.

The modem is set to "IP Passthrough" but I could not figure out how to set up the "Cascaded Router" setting so that the modem is better configured for having a second router attached.  But I also had not changed any settings on the modem for nearly a year before I started having the daily router crashes.  I tried disabling the modem firewall settings, but it made no difference.  Many of the "Invalid IP Packet" entries initially were showing IPv6 addresses, so I tried disabling IPv6 on the modem, in case there was some conflict, but it did not help.

I think it is likely that some firewall setting or some setting that conflicts with my Netgear router is causing this, but I cannot pinpoint it, especially since, as I mentioned, I did not change anything on the modem when the issue cropped up.  Have you experienced this issue?  Do you have any recommendations for better configuring the modem to simply be a passthrough to my Netgear router?