sft-1200 connected only 100mbps

I purchased the sft-1200 opal a few months ago.
However, I discovered that one of the two LAN ports was only connected at 100mbps.
I tried resetting it, changing the LAN cable, and changing the firmware, but it didn’t help.
I want to know what the problem is.
please help!

So when you put the same cable to LAN2 or LAN3, it is 1000Mbps?

right. Even if I test with the same cable, the results are the same. That’s why I posted.

Is your LAN cable capable of 1 Gbps?

of course. I tried. With cat5e, cat6, cat7 cable.

Seems nothing to do. Maybe just exchange and see.