25 year old website disappeared from Bing

Hello,

Our brand website has ranked fairly well on Bing since Bing first opened. The site has existed since the year 2000. It has usually/often ranked #1 for the brand name and closely associated terms. We often had a full array of image and page links accompanying our listing even when that listing was not #1.

Recently we've noticed that our top ranking home page & category pages have all disappeared from Bing and only a handful of  deeper, somewhat obscure pages of the site are showing up & they are ranking very poorly (round page 3-5) with no image or page links accompanying.

I've gone through Bing Webmaster Tools (and many other tools) and the site is healthier than ever, nearly 100% scores across all metrics, zero errors, very few warnings or suggestions. The site is modern, responsive, updated regularly & recently etc. 

I can't figure out why our normally top-ranking pages seem to have been purged from the results and only more obscure pages are coming up at all. The pages seem to be indexed, just not showing up anywhere anymore.

Any Insights would be greatly appreciated.. Thanks.