Needs to be bug fixed on the engines end afaik, others have been running into it without the plugin as well, since 4.19 is a preview build its not the largest deal unless it releases with it still broken.
There is far too much incompatible across 4.18 and 4.16, Epic changed a lot of the back end. You could start with the 4.16 build and cherry pick features from the commits to add to it, but I don’t specifically support all features backwards. A lot of the additions require/d deep character modifications to do and so they would have to be re-written for older engine versions.
If it is something like the interactibles or the gesture component, those should just slot right in without a problem.
Although, while 4.16 was the most stable, I still consider 4.18 the “best VR patch” so far.