I seem to not be able to create private networks, after some testing if i switched from survival to creative the private network shows up but after switching back to survival mode it disappears again.
Controlling my save with NBTExplorer i found out that the UUID was wrong? If i set the UUID to 0 in every network that i created, then the networks in the game would show up in survival mode too. So i tried the opposite, modifying my player UUID to be the same as the one used by the network (which seems that is always the same and doesn't change) but with no luck because after joining the save it restores to the default value which is 0.
Initially i thought that it could have been caused by some mod conflicts but even when loading only Flux Networks + JEI it still manifests this problem.

I also can't create any private or restricted network in Version 1.12.2-3.0.13 at the latest Version of the Continuum Modpack

FTB Revelation 2.1.0 modpack, cannot see private or restricted networks. Didn't work on modpack version 2.0.0 too. Giving myself Operator fixes the issue.
Tested on Dedicated Sponge server.

I can confirm this is happening on both Revelation (2.1.0) and Continuum (1.3.1). Both are public multiplayer servers and running spongeforge.

Is this a SpongeForge / Flux Networks clash? Anyone experienced with just MinecraftForge?

Fixed: The next version will hopefully prevent this happening, please open a new issue, if it returns.