Desktop Average Position is dropping dramatically, but mobile/tablet remains consistent.

Like others, we've noticed a rather alarming continuous drop in Google organic traffic that began like clockwork on July 1st, then again at the end of July (call it the last week of July).

It seems like we keep going down, down, down. :c) When reviewing Search Console it's apparent that this drop is isolated to Google > Organic > Desktop SERPs. So no de-indexing of content (which is typically our problem), and no fluctuations with mobile SERPs, just desktop.

We've never bought links nor done any grey/blackhat techniques, and no code changes were pushed that would impact technical SEO. We have had a great number of scrapers target us over the years (lol you should see our blacklist IP list) and have been 'victim' in the past (read 3+ years ago) of various comment spammers including links to us. I figure this was negative SEO attempts but since G now discounts and doesn't penalize I doubt this is our problem.

I've searched around without finding any quality articles that have investigated why desktop SERPs would vary so much in comparison to mobile (FYI tablet has consistent SERPs too).

The best I can guess thus far is that other websites that had been previously penalized for 'bad' links recovered as a result of this update. Thus pushing our average DESKTOP position from 9 or 10 to 17(!). These same websites that are now recovering must not be mobile optimized like we are, hence no impact to mobile.

What say you Sage community members? Any other ideas why desktop placements would drop so much when mobile/tablet remain consistent?