Thanks, that helped.
So, I have determined that the code was stuck on an ACF code part, where the get_field_object() was called. I googled around, and it turns out that this particular ACF function is problematic, and caused issues to others as well.
I have added a quick bypass for now, so it’s only called when needed. I will add a permanent fix for the upcoming release. The search should work now just like before.