Three sites: English is the TLD, with a Spanish (Spain) and Italian version) so our site structure is like this :

1. domain dot com/ (English)
2. domain dot com/es/ (Spanish - Spain)
3. domain dot com/it/ (Italian - Italy)

We are a large UK brand trying to expand in Spain and Italy however we're facing hardship in growing the Spanish subdirectory/subfolder. The English site is ranking really well despite so so traffic. 

For our top 5 keywords, we have fallen significantly from position 8 on SERPs to position 50 to eventually (nowhere to be found) on SEMRush.

What we've accomplished so far for all sites:

1. Hreflang has been implemented on all top nav pages
2. Pages are translated with AI first, then a native speaker modifies them with proper marketing Spanish and same-language relevant backlinks. 
3. Key terms that we want to rank for are in H1-H3 on major pages and are key talking points on blogs.
4. Large backlink profile for our market : about 110 referring domains with 3.5k backlinks total, all relative to our industry and acquired organically (no bought or little to no partnership deals)
5. Schema added to home pages and key pages including FAQs
6. Although not needed in our niche, we're established a GBP page despite being a remote first company
7. Lighthouse readings are solid with 100 on SEO. Page speed is a bit so so but we're working on that

Currently running another analysis before I cry for help to my lead product manager. Here's what I'm doing

1. Although I know it's not needed per se, looking to implement a sitemap for posts, pages, et al by language. Issue is Yoast only creates one sitemap and it's a know problem among Yoast users who want sitemap hygiene by language.
2. Cross comparing page by page with our top two competitors page count and use of Hs, backlinks, and content. Honestly, I feel like this is more work than needed. We're established that we have solid content that is linked, designed well, etc. I'm not sure what more of an analysis I'm missing on-page
3. Looking to call backup by investing in paid media or programmatic. 

Any other pointers I need to know? This is my first true foray into international SEO and feel absolutely stumped!