Hello Jan,
No luck, tried once more. The only thing what is communication with the motherboard, is the firmware update utility.
It seems fw update runs fine to 2.2e r2.
But after that there is no communication with fmscope. FM Scope opens the com port or network com port, but there is no data coming from the device.
Tried with two different devices.
Disassembled it, tried the connection between motherboard and ethernet to serial board with multimeter, the connection is ok.
There is no oxidation sign, even there are no bird's nests or mouse family integrated

, everything is clean and tidy.
FM scope is 1.7.1, OS is win11 pro x64. Lantronix version is 7.0. something, did not try to update it.
Tried with two different usb to serial converter.
I did not tired with micro usb cable.
Any idea to test? Maybe an online video call (viber or so?)?
Next day I may be take my oscilloscope, what can decode RS232 (never tried yet), and I may check the data pins of converter.
Best
Peter