When using flux networks version 1.2.6, whenever I make a new network that is public and add my friends, and then I leave the chunk for a second, when I come back the network is deleted, but when I make a private network, it works. Any fixes?

Try 1.2.8

same issue on the latest FTB Beyond version, includes "FluxNetworks-1.10.2-1.2.5". i'm on a semi-private server, i can not update until all users are ready to update.

Lots of changes are made between updates. If you can't update, there is nothing you can do.