do teleport tether have a limitation or is this a bug
we got 5 working in the Overworld
and 1 in the nether
when i add one more to the Overworld f10 dont show it and then i unload the chunks there dont like it's working

Minecraft version 1.7.10
Minecraft Forge version 10.13.4.1614
mod version 4.7.7
buildcraft version 7.1.23

are you playing on a multiplayer server?
they usually have limitations on how many chunk a non-op player can persist