I was able to confirm this issue and that it is a known issue. I went ahead and sent this information to developers. I do not know a ETA on a fix for this at this time. hopefully we can get it fixed soon.
Hi David Thank you for your reply immediately. I am writing a ProRender
article in a Japanese CG magazine, so it would be very helpful if you could
make a fixed version. Thank you. TomoG
2019年5月6日(月) 23:18 david_s <firstname.lastname@example.org>:
Re: Difference in roughness of transparency in final rendering and
viewport render. in ProRender
Try increasing the Max glossy to around 8. It should give better results.
In the viewport and IPR rendering, there are 3 parameters only that are located in the system tab - Viewport and thumbnail settings. While the Production render actually uses the Quality tab.