Searching across the forum I came across this topic below on the subject which is a few years old at this point.
viewtopic.php?f=30&t=59386&p=304239&hil ... og#p304239
It seems that this glitch still persists in Octane 2021.1.5. Is there any plan to fix this for the future? The mesh + specular material with a medium is alright, but with animated VDBs becoming more common, I think it would be nice to be able to use objects with transparency inside of volumes without having a weird border around the object.