that was the latin "ad" aka "about"
mobile friendly tests fails see https://search.google.com/test/mobile-friendly/result?id=SAu...
and google can not render the page correctly
also test with GSC page inspect -> render page -> see screenshot
if this correlates with the software update (and the page URLs) did not change, then this is the strongest contender.
check the crawling metrics in GSC google search console
js, css average load time should be max 200ms- or it is some other asset delivery issue
html not more than 400ms average response time
note: i am the author "understanding seo" https://gumroad.com/l/understanding-seo/hacker-news (think seo for hackers) feel free to mail me, contact in profile
everything points either to an page URL change or 4 SEO tests issue - from my point of view
written on a mobile in the metro, so can not check in detail right now