Unfortunately I can only repeat myself here. As long as there is not 64 bit support from UAD, there are only disadvantages using them “bridged” in Renoise, and you will sooner or later run into other problems. So please stick to the 32bit Renoise versions for now.
The other thing is that we don’t have an UAD for testing purposes here, so we can’t really help you out at the moment. UADs are very special plugins which always need a bit of extra work and testing, so we will ask UAD for assistance in future.
It’s also unlikely that this is a new problem in B6, because we don’t really have changed anything in our plugin host implementation. The post linked above basically matches your report and this was a report for one of the previous betas, not B6.