I recently noticed my two L3 switches were no longer seen in Opnsense.
Initially, I though it was something silly like an order of operations on the signal side, but then started to dig-into it a bit and found Opnsense truly could not see the switches(ARP, ping, etc)
And so knowing I was not entirely crazy, I reinstalled Opnsense and sure enough, found that both switches were present and account for
I then proceeded to update Opnsense, and low and behold, they disapeared again
And so my question now is, what the heck is going on here? lol
Autonegotiation issue ? What happens if you set the port speed manually on the FW ?
A bit of detail on what you're using on both ends would help, like driver/interface on the OPNsense side and if at all possible on the switch.