Hello Sam,
same thing here. The output is now a way darker then before. I know you play around with the stereooutput 360 module as well, here i have to put all lights double in power than in 4.13. So something must be changed. Even with skylight or hdr you have to double the intensity for the output. In Editor it is fine, or in this case overbright. So you don´t have controll for the lightning as you always have to guess in the editor and then render and see if this was enough intensity. Didn´t you see this too? Just place only a Pointlight in the scene and do the test, you will see it clearly. Thanks for an answer. 