Been troubleshooting this decline for months. About 6 months ago, before I started paying attention, AppGoblin had no meta headers, no canonical pages, and no SEO optimization of any kind. Many pages routinely took 10 seconds to load.
At some point I took an interest in growing the site, it honestly only gets a few users a day at most, but I enjoy working on it and think it’s interesting. I added it to Google Search Console and started trying to get the SEO ‘best practices’ started. This somehow led to a steady decline to the point where nearly the entire site has been deindexed from Google.
It’s quite ironic that the site seemed to do better before I started following SEO best practices (Header meta tags, keywords, descriptions, faster loading pages, and adding page to Google Search Console). Of course, since it’s a fun hobby site, I’ll just keep plugging away at the problem, so hopefully one day I’ll figure out what the Google issue is.