BungeeGuard setting breaks Forge 1.12 compatibility

Steps to reproduce:

1. Setup proxy and one modded forge backend server
2. Set proxy to announce-forge to true, ping-passthrough "mods", and forwarding mode to "bungeeguard"
3. Attempt to connect with BungeeGuard installed on backend server

Expected result
Successfully joining the server

Result encountered
Disconnect from backend server saying "this server requires mods"

Additional notes
WaterFall + BungeeGuard does not reproduce this error. Additional testing using VelocityGuard and setting forwarding mode to "legacy" works. My thought is that the proxy is not relaying the client mods to the server when set to "bungeeguard" mode as the client presents as a vanilla client even though mods are installed. When set to "legacy" the mod list gets passed to the backend server. The proxy is able to passthrough the mods to the client but not able to send the client mods to the backend server.

Velocity Version: 3.1.1

Start by reproducing the failure with Velocity 3.1.1, announce-forge, ping-passthrough "mods", bungeeguard forwarding, and a Forge 1.12 backend. Compare the bungeeguard and legacy forwarding behavior, including the Waterfall and VelocityGuard observations. Done means a modded client can join the Forge backend with bungeeguard without the backend reporting that mods are required.