Add NodeManagerScopes to fix use-after-free issues (#4768)

Add NodeManagerScopes to fix use-after-free issues (#4768)

This commit fixes our current ASan issues. Some methods in `NodeManager`
were not creating a `NodeManagerScope` for `this` but were indirectly
calling methods that get the `NodeManager` from the current scope, so we
ended up calling methods on a `NodeManager` that had already been
destroyed.