I already posted this question on Answerhub, but got no answer so far.
As far as I understand, diffusefromcapture=1 allowed to use ReflectionProbes as IBL probes, affecting the actual lighting of the diffuse/albedo. Now in 4.8-3.9 this console command simply increases the reflection contribution, leaving diffuse untouched. I tested it in 4.4.3 and it worked, but I really need it for the newer versions - 4.8-4.9. Can it be done?
On a side note - is there at least some consideration for IBL in UE in the future?