:sort -r date doesn't seem to update the UI at all but does say "Sorting complete".
This happens when the remote server doesn't support the extension. We need to disable :sort in that case instead of just ignoring it when explicitly sorting.
Gmail? Sort is not supported on gmail.
We don't handle the case well where the sorting is unavailable, we simply fall back to not sorting.
I'm having the same issue using protonmail. (just setup aerc for the first time)