RestMiddleware.Unreachable was implemented as part of #2873.

However, Unreachable can end up being an unhandled exception when propagated from - https://github.com/nucypher/nucypher/blob/development/nucypher/network/middleware.py#L155. For example it's unclear that it is handled here - https://github.com/nucypher/nucypher/blob/development/nucypher/network/nodes.py#L803. There may be other areas as well.