We have a similar sort of set up, a main router and a second one configured as a wireless AP at the other end of the house, originally done to have to kids on a separate network which could have its internet filtered separately and configured to remove the internet at night.
The two network ranges are entirely separate (the main one is 192.168.0.xx and the second one 192.168.1.xx) and devices connected to the second one can't print as the printer is on the first one (same goes for if your phone connects to the second one and you try to cast/send Youtube to the TV, because it's on the main one). The wireless AP is manually set to route all Internet traffic to the main one - which confusingly means it has a manually assigned IP of 192.168.0.200, even though the IPs it gives to devices connected to it are 192.168.1.xx (and they see it as 192.168.1.1!) All very confusing, but you have to think of the IPs (and network masks and so on) as which "side" of the network junction/connection they are on.
Wifi is notoriously difficult to troubleshoot, and wifi printers even more so, as they are printers, which are the tools of the Devil
The only cure may be to get the printer to connect to the main router wifi, (and make sure the relevant computer is too) which may mean physically moving it very close to it, not exactly convenient!