@wjmeier 

Have you tried updating the firmware?  Where do you live?  The US version of the AX1800 does not have the router version or firmware version you referenced in your post.  However, it does appear to be a little old.  

Has the router been stable otherwise?  The only other thing I can think of is the power supply is going bad not providing a stable DC voltage input.

I am in the US. The router indicates it is up to date on firmware. It is also set to automatically update.

I will look for another power supply to see if that works.

I replaced the factory 12V 1.5 A power supply with a 12V 2.0 A power supply.  Hopefully, this will stop my problem.

I have a USB device connected and every Ethernet port in use.