From your diagram, it is obvious that Printer/Copier/Users communication occur on the Dlink Switch. In this case, the RB951 router will not interfere with your LAN communication since it is used to route packets egressing your LAN. You don't even need to add any bypass rule for the Printer/Copier in hotspot. I suggest you place more attention on the Dlink Switch.
This is true for normal IP communications, but when there is a hotspot, this is not true. The hotspot will do things similar to netcut so that it will interrupt all communications from LAN hosts / redirect them to itself and a hotspot webpage. (it answers all ARP requests, for instance)
I do not know what port and protocol of the Copier device used. (RICOH AFICIO 2075)
Check the hosts table and see if the printer is appearing in this page at all. See if it has any other IP in "address" -
IP Address is the real actual address a host is configured with
To Address is a pool address the Mikrotik assigns to the host - it tries to use the same as the real IP address, but they aren't necessarily the same - if they're different, you talk to the device using "to address" (this is a feature to allow Internet access on devices where the user has no permission to change the IP address settings)
Check the hosts list when the printer is reachable for two minutes, and check again when the printer is not reachable. Chances are, it will have timed out from the hosts list. If the printer sends no traffic, then it will not be recognized / added to the hosts list.
I had a problem (unfortunately I never could solve it) where certain model Dell switches would not be recognized by the bypassed host configuration such as yours. If I would log into the switch by some means that avoided the hotspot, and then ping the default GW, the hotspot would add the switch and everything would work until the timeout went by. If I did not do this, I could not ping the switch from the Mikrotik, no matter what I did....
If you can't get it working, then I suggest you create a second WLAN, associate a VLAN tag with this wlan, and connect the printers to the second wlan - this second wlan will not have any hotspot on it, and you would put the printers' IP addresses in the walled garden so people could print w/o logging in to the hotspot.....
) so what was I did was that I remove the "Address Pool" from my hotspot server, so there were one-to-one NAT, no IP change at all so my bypass work correctly....
