After replacing the fans in my ICX7250-48P with the quieter ones recommended here, I just moved all the network connections from the existing unmodified ICX7250 to the modified one, with exactly the same configuration, vlans, etc. Strangely, the network link to my proxmox node via a sfp+ goes down when I moved the sfp+ connector to the modified switch. When I move the sfp+ connector back to the unmodified switch, the link comes back on again.
Any idea what I have missed?