1. any debugging information generated in a thread's pageContext is lost (i.e not merged into request pc)
the debug info is very likely to be duplicated, especially with implicit access logging, which simply stops logging
after 1000 items
2 unscoped, thread scoped variables aren't being resolved inside a thread
3. implicit scope access, reports thread scope when accessing a thread scoped variable within a thread?
I've checked this ticket and confirmed the issue has happened on a thread. Yes, it throwing an error for the unscoped variables in a thread. But, ACF works fine for this kind of scenario.