I expect you have the forge support config option turned off, that will cause your client to wait for a packet that never comes. That should be sufficient.
However, I would suggest (at least at this stage) using Waterfall instead as a drop in replacement for Bungee, it’s basically Bungee with loads of compatibility patches for Forge and other enhancements. You will still need to turn on Forge support if you reuse your Bungee config.
Alternatively, there is Velocity, which is another replacement for Bungee but is completely new. It is in alpha state, but has recently seen Forge support added. Certainly when 1.13 comes around, I would suggest using Velocity once it gains support for it.
In both of these cases, you don’t need SpongePls.