With the switch to using the primary CUDA context (4f58cffb4e) it became possible for peer access between CUDA devices to already have been enabled for that context, either by a previous Cycles session or third-party library, thus causing the call to "cuCtxEnablePeerAccess" to return "CUDA_ERROR_PEER_ACCESS_ALREADY_ENABLED". This is not a failure state however, so just needs to be handled like a success return value.
Patrick Mours