It seem that using the built-in NZBGeek Search provider was not finding any results (although I had a 2nd and 3rd provider that often find items and so I didn't really notice this issue for quite a while). But I was able to easily find the results through the manual search on the NZBGeek site. To test things, I added custom Search Provider "NZBGeekCustom" using my same API key and the url "https://api.nzbgeek.info/" and my desired categories. I then removed the default NZBGeek from my search provider list, and added my newly crated custom one; then forced a backlog search and a bunch of stuff that was not found was suddenly found and started to DL via my client.