Can't connect after IP change

Hi, Reddit! I'll explain the situation the best I can, I don't know which details are relevant.

I have a bunch of ethernet-based thermal printers, that have been configured to use different ports. I also have a server running an old-ish version of Linux in another subnet, that sends the print works. Let say the server is 192.168.0.2, and the printers are 192.168.1.101:9101 and 192.168.1.102:9102. There is no fancy firewall between subnets, everything is transparent. Life is good.

Then, the first printer breaks. Due to COVID, the second printer is receiving almost no work, so I decide to exchange the printers. To avoid messing with the server's configuration, I just reconfigure the printers, exchanging their IPs and ports. This is done in an isolated router, so no IP conflict at any time. Put the printer back in the workplace and... it doesn't print. The server can't even ping either of them. I can ping them from both subnets, only not from the main server. The server also doesn't have any fancy firewall nor anything related to the printers. Being an emergency, I just reconfigure the printers back, and change the server's configuration. They work.

I even tried restarting the server, to no avail. Any guess on what could be the cause? Maybe some cache-table that needs cleaning? I have no idea.