An observation
The printer is likely showing offline in dashboard because it isn't passing any traffic. Once it starts passing traffic it will show up as an active client. Once it stops it will likely go "offline" in dashboard. Totally expected behavior as we use traffic as a way to determine if it's online.
Some suggested avenues of troubleshooting. I apologize if this is above your comfort level, this is a public forum so I'm trying to include as much information as possible in case others might benefit. If that's the case you might go ahead and speak with Meraki Support.
Checking settings
Does the printer have an IP address? Is it set to use DHCP?
You mentioned you're not seeing a lease in dashboard, what about from the printer help page?
Can the printer IP be set manually?
Is it the correct IP address according to the vlan that you have it in?
Is your MX port configured correctly? Probably easiest setting it up as an access port with the same vlan as all your other clients.
If you're still in port 2, make sure that it's not configured as an internet uplink.
Verify connectivity
Are you able to ping the printer?
Are you able to access the printer's web interface? (assuming it has one)
Troubleshoot the printing problem
If you're familiar with Wireshark I would suggest you take a packet capture on the LAN interface of the MX with a filter expression of "host IPofPrinter" (it might just be easier to start by taking a packet capture on the wired computer). See how it's communicating, and the type of traffic that it's sending. If you're not familiar with Wireshark, now might be a great opportunity to take a peek at what's going on. If you check out my Wireshark community post, I have some information about getting started. Based on the age that you mentioned, the thing that I would be interested in most is seeing if the computer and printer can form a TCP handshake: SYN, SYN-ACK, ACK. It could very well be some other method that you'd need to find from the manufacture.
To troubleshoot why it isn't getting an IP, we need to see all the communication on the LAN. So I'd recommend a filter expression of "not host MYcomputerIP.
Meraki Support can certainly take a look as well, to make sure everything is set up correctly. Probably best done by calling so we can troubleshoot this live. Based on that, they'd be able to give you some more specific next steps.
Footnote. The reason it might be easier to take a packet capture from the computer is that when you're doing a LAN capture (and aren't using a filter expression) on the same MX that your computer is connected to, is because otherwise, you start capturing that capture of your capture. It's recursion all the way down to a very large file and likely a failed download. So when you're on the LAN of the MX, it's always best to use a filter expression of the device you're troubleshooting or "not host MYcomputerIP".
