The thin client does not connect to a wireless network with hidden SSID.
An option in the thin clients' network configuration is missing.
The current IGEL Universal Desktop Linux v5 manual describes in detail how to connect to a hidden wireless network.
For older versions such as Universal Desktop Linux 4.12.100, 5.01.100 and 1.06.100 (SoC):
IGEL's Terms & Conditions apply.