THIN Client Network Failure

i am struggling with getting my THIN Clients connected to the network.

Type of THIN Client is 15 inch PRO (6AV6646-2AB21-2AX0).

The THIN Clients network port has very strange behavior. Its leds are off and when i unplug the network cable they light up. Sometimes when i restart the THIN client several times with unplugged network cable and then connect it when THIN Client is booted it connects to the network and responds to ping. When i restart the machine in this state it doesnt connect to the network after the restart.

THIN Client has static IP. Restarting the port on CISCO switch sometimes helps and THIN Client connects to the network. But again, restarting the THIN Client disconnects it from the network.

Can this be switch related? I have multiple THIN Clients connected to one switch with same behavior.

THIN Client has static IP, i tried uploading new firmware via web interface but it failed. I can add the log file later. It has 1.4 firmware in it.

i tried different switches with different firmwares (CISCO, TPLINKs, ZyXELS)

Mentioned thin clients connect in one of 10-15 restarts, but connection is lost after i reset the TC

One of my THIN Client has both LAN leds on all the time, whether there is a cable connected or not.

How strong is the network card on thin client? My laptop, or 477C can connect on 90m cable (stable connection), but this thin client fails, leds on LAN port are off. when i connect the 90m cable to another switch and then to thin client it works.(with 50% packet loss)