Bizarre Behavior - Canon MX-850 WIRED printers not seen on network.

> [...] The printers work fine with the older router but neither is
> accessible on the R7000. [...]

Define "[not] accessible".  Are you looking at an Attached Devices
report on the R7000, or what?  As usual, showing actual actions with
their actual results (error messages, LED indicators, ...) can be more
helpful than vague descriptions or interpretations.

> [...] The printers are ancient, but they should still show up with an
> IP address when hardwired to the router. [...]

   "show up" where/how, exactly?  LAN Ethernet port-status LED
indicators?

   What is the LAN IP address of the old router?  What is the IP address
of a printer when it's connected to the old router?  Is the printer
getting its address "automatically" (by DHCP), or did you give it a
static address?

   What's the LAN IP address of the new router?

> [...] The router has the latest firmware. [...]

   It's probably unimportant in this case, but, as always, an actual
version number would be more useful than your opinion of what's "the
latest available" today.