Check network cable firmly plugged in and port functioning. Verify PXE enabled as first boot in BIOS, try disable/re-enable. Could be faulty network adapter or motherboard dropping connection - may need hardware troubleshoot/replacement if persists on one unit. Confirm ThinManager server address/port correct. Try different server. Re-image PXE partition to rule out corrupt boot image. Check event logs for clues on disconnects. Since other units working, likely hardware or boot issue on this endpoint. P.S. My imho of course