The method is called from storage_proxy::mutate_hint() which is in turn called from hint_mutation::apply_locally(). The latter is either called from directly by hint sender, which already runs in streaming group, or via RPC HINT_MUTATION handler which uses index 1 that negotiates streaming group as well.
To be sure, add a debugging check for current group being the expected one.
Code cleanup, not backporting
Closesscylladb/scylladb#28545
* github.com:scylladb/scylladb:
hint: Don't switch group in database::apply_hint()
hint_sender: Switch to sender group on stop either
85dcbfae9a