Could not unwrap first stream message

[rejuvenile]

Some of my RBE executions result in the following message server-side:

2025-03-03T19:52:08.641989Z ERROR nativelink_service::bytestream_server: error: status: Internal, message: "Error receiving first message in stream : Could not unwrap first stream message", details: [], metadata: MetadataMap { headers: {} }
    at nativelink-service/src/bytestream_server.rs:641
    in nativelink_service::bytestream_server::write with request: Streaming
    in nativelink_util::task::http_executor
    in nativelink::services::http_connection with remote_addr: 192.168.191.244:51500, socket_addr: 0.0.0.0:50051

Another manifestation of toolchain issues? My builds do not fail.