SERP position high, but traffic low after a site redesign?

Currently working in Saas SEO and we just completed a redesign two months ago. Given the project we knew to take precaution on redirects, content optimizations, and internal linking. That's all squared away. Our issue not is that our traffic (unexpectedly) is down nearly 60% as of today. Technical and design SEO is still being worked on as Lighthouse SEO scores are trash (SEO: 39, FCP: 64) We are however still maintaining strong rankings in the SERPs (Google and Bing) for our top performing keywords. Has anyone ever experienced this?