For me personally, I started doing a lot more development with TestStand when I started my new job 2 years ago. Since I had zero TestStand experience most of my time/energy has been spent coming up to speed on TestStand so I was over at the NI forums for that. My need for advanced LabVIEW topics has been very small and my need to pose a question that has yet to be asked is even smaller. I have found that my questions have already been asked by someone else in the past so the need to create a new topic is far less than before.
That does bring to mind a thought...search engines have become much more better over the last few years and on top of that people have become better at forming queries for search engines too. Perhaps we see less new topics been created because the existing one's answer the questions sufficiently and the users can use that to answer the question. Can you get a plot of # of views of a topic? Or maybe updates to old topics?
I also love LAVAG for my LabVIEW questions. I want it to stay.
Answering the specific question posed, the only other space (other than NI.com) for LabVIEW content is the LabVIEW Maker Hub (https://www.labviewmakerhub.com/). Its less Q&A for issues and more neat projects type of stuff.
In my personal time I find myself spending more time with the Raspberry Pi and Arduino related forums because it's relevant to the toys I am using.