span-lite | span lite - A C++20-like span | File Utils library

There range library probably doesn't know that nonstd::span is a view. You need to tell it by specializing ranges::enable_view. Without that, the range library thinks it's something like a vector, and when you pass an lvalue of it to views::all you get back a view that references the local span object rather than a copy of the span.

In the recent past, range-v3 would have used a heuristic to guess (correctly) that span was a view, and your code would have just worked. It changed per request by the C++ Committee, which didn't like the heuristic. To be fair, it would sometimes guess wrong.