The reverb in the old engine was not supported on every platform and on ones where it was supported, were different sounding for each platform. That is because the reverb was an effect created by that platform. So on Windows and XBox, it was Microsoft’s own XAudio2 reverb effect. On PS4 it was Sony’s NGS2 reverb. On Mac is it was Apple’s AudioUnit reverb.
The New Unreal Audio Engine is Epic’s Reverb, it renders within our own DSP pipeline, and so it will sound exactly the same on every platform you deploy to–the old one will not.
As far as redesigning the old Engine Content, we’re aware of this issue and we’re looking at the best approach to take.