There is an unexpected difference in lighting between deferred and forward caused by an incorrect render of the shadowmask in the GBuffer (_GBuffer5). Not sure if this is the only cause or only part of it.

Attached images for expected vs actual

Steps to repro:
# Download and open the repro project
# Find the renderer in the settings folder
# Swap it's rendering path to forward and see 2 shadow masked spot lights appear

Disabling the main directional light (which is taking the red channel of the shadow mask) and rebaking will free up the red channel so one of the spotlights will be working instead.