Your hreflang says English-only. Does your language switcher agree?
I run a maintenance sweep over my own site every day. Yesterday it found 1,474 dead internal links that had been sitting there in plain sight, on 737 pages, and every automated check I had was green. The cause is a bug class I have not seen written up, so here it is. Two places encode "which languages does this page have" A partially translated site has, whether you planned it or not, two…
We haven't written up this one. Dev.to has the full story — the link below goes straight to it.