Ubiquiti EdgeRouter X no link state problem


At first, thought it was a bad ethernet cable, but it's not.
ER-X connected fine on WAN-port to Genexis FttH modem. After few minutes, link gets dropped.
Warm reboot, cold reboot... doesn't matter, no morel link state.

Switching ethernet cable to any other device, all works fine. Connecting ethernet cable between different (non-ER-X) router to FttH works.

Back to ER-X, so at first it worked a couple of minutes. Suddenly it stops. No output in log, only that swconfig shows no link state on the WAN port (0).

Anybody got an idea whether this is a driver problem with MT7530?
This is only output in log during boot, port #3 belongs to computer, port 0 is connected to FttH but no link state:

Mon Feb 20 17:13:46 2017 kern.warn kernel: [ 1.660000] [mtk_nand] probe successfully!
Mon Feb 20 17:13:46 2017 kern.info kernel: [ 3.120000] mtk_soc_eth 1e100000.ethernet: loaded mt7530 driver
Mon Feb 20 17:13:46 2017 kern.info kernel: [ 3.130000] mtk_soc_eth 1e100000.ethernet eth0: mediatek frame engine at 0xbe100000, irq 10
Mon Feb 20 17:13:46 2017 kern.info kernel: [ 5.030000] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up

Any help is appreciated.