My 4-way switches work correctly. I would like help figuring out where the power is coming in from and where the light fixture is (at the end, after a certain switch, etc.) I'm also trying to understand what is happening in this electrical box where "switch B" is housed--there are 4 cables entering the box. The green line represents the white wire.
Your setup is quite improper & illegal. So, don't touch or change anything unless you're rewiring all of it correctly. The 4-way switch (B) just connects the 2 3-way switches (A & C), it's just a bridge.
FYI, the wires with 3 wires total (black, white & ground) are supposed to be solely for the power supply (C) & light operation (A), just regular Romex cables for in & out. The wires with 4-wires total (black, red, white & ground) are usually just the 3-way switch connectors. They aren't supposed to be the power supply nor light operator & should just transfer the power from 3-way switch to 3-way switch through the 4-way switch.
Your problems are that Regular 3-wire Romex (cable 4) was used to connect (C) to (B), instead of a 4-wire cable (cable 2). And, a proper 4-wire cable (cable 3) was misused to connect (A) to (C) while also operating the light. Due to these you can't even label things uniformly.