Orbi AX4200 (RBR750) logging incomplete / very sparse; rolls over very quickly

Yes, logs are not very helpful and can be sparse. I uncheck most of the log entries if there not needed. Sometimes enteries are good sometimes much less. Not much we can do about them. 

My (older RBR50) Orbi log contains those DHCP and admin access entries, but fills up with "DoS Attack" messages.  The rest of the log options are for things that almost never happen on my system (VPN access, access to allowed sites, access to restricted sites, port forwarding, etc.)

Netgear changes default firmware settings on each new model without explanation.  It could be that your model no longer reports DoS Attacks. There was never much point to those log entries, so maybe someone decided they were no longer needed:

• DoS attacks cannot be stopped, just as robocalls and junk mail cannot be stopped.
• The Orbi does not accept any of these connection attempts, just as we can choose not to answer phone calls or open junk mail.
  (I bring in the mail and stand over a trash can. 90% goes directly in the 'round file' without being opened.)
• Scanning for DoS attacks does consume some processor capacity (not much, but definitely some).

My old Orbi has an option in the WAN Setup menu to disable DoS scanning.  I do not know if your model has the same option.

I am a bit OCD, so I have the Orbi email me the log each time it fills up. I cut and paste each email into an Excel spreadsheet. Each log file is 231 lines.

Sounds like confirmation that the logs are pretty useless on the Orbi. I'll add it to my list of gripes about this product. Maybe part of Netgear's strategy to require a support contract. :smileywink: