Tell HN: A case of negative SEO I caught on my service and how I dealt with it
I'm sorry to say, but the neg SEO didn't drop your rankings, it was to do with the Google algorithm update [1]. Check the screenshot from Ahrefs [2], and your traffic drops on 3rd of December which is when the update went live. 
[1] https://moz.com/blog/googles-december-2020-core-update
[2] https://i.imgur.com/DBkdUEk.pngGoogle's algorithm is smart enough to recognise Neg SEO attacks. Sure five years ago you could buy a blast of spammy links using Xrumer or GSA with some viagra anchor text and boom you're competition is gone.From a quick glance, most of your pages have pretty thin content, and I assume it's pulling from an API, so none of it is unique. If there was one thing I would do is try to build some content on pages. A great tool to analyse and develop content that is SEO friendly is SurferSEO - highly recommend it.I'm surprised your forum doesn't rank as well as your main site as it looks fairly active. However, I'm not sure about how PunBB does SEO wise.