Make sure there is no space after the comma.
192.168.2.0/24,192.168.3.0/24, not 192.168.2.0/24, 192.168.3.0/24.
192.168.0.0/16 should also work.
See [HowTo] Use Plex with No Internet
You may need to add entries for List of IP addresses and networks that are allowed without auth. Be aware that while it bypasses the need to login, it also gives any such devices full admin access to the server. It also means any age, content, etc restrictions are not enforced.
