Thanks to @jon_eg , it turns out 1 material was causing the problem in this scene. The clothes material has a subsurface node that - in my scene - had a multiplier of 1.5. Reducing this value to 1.0 fixes most of the problems but still some white splotches are visible on some edges of walls. Removing the subsurface settings for this material altogether results in this image.
Tested on the current 5.0.0.p2. Strange thing is; in the output log it still reports ‘static lighting system is removed from world lightroom_day’
Going to convert some of my own projects asap and test again. Really hoping it works as well…
