Gradual Drop in GWT Indexed Pages for large website

[ArashG]

Hey all,

I am working on SEO for a massive sports website. The information provided will be limited but I will give you as much context as possible. I just started digging into it and have found several on-page SEO issues of which I will fix when I get to the meat of it but this seems like something else could be going on.

I have attached an image below. It doesn't seem like it's a GWT bug as reported at one point either as it's been gradually dropping over the past year. Also, there is about a 20% drop in traffic in Google Analytics over this time as well.

This website has hundreds of thousands of pages of player profiles, sports team information and more all marked up with JSON-LD. Some of the on-page stuff that needs to be fixed are the h1 and h2, title tags and meta description. Also, some of the descriptions are pulled from wikipedia and linked to a "view more" area. Anchor text has "sign up" language as well.

Not looking for a magic bullet but to be pointed in the right direction. Where should I start checking off to ensure I cover my bases besides the on page stuff above? There aren't any serious errors and I don't see any manual penalties. There are 4,300 404's but I have seen plenty of sites with that many 404's all of which still got traffic. It doesn't look like a sitemap was submitted to GWT and when I try submitting sitemap.xml, I get a 504 error (network unreachable).

Thanks for reading. I am just getting started on this project but would like to spend as much time sharpening the axe before getting to work.

lJWk8Rh