A CodeChain node keeps emitting "sendError"

This phenomenon was found on 2019.12.17 at about 2 P.M.
The monitor sends a codechain death confirmation because the node monitor that was watching had been dead. The log is like the following:
```
#364967762 2019-12-17 05:37:18.685152917 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:19.224282592 UTC P2P Worker #1 WARN netapi block-propagation cannot message Global 34.85.31.119:3485: "SendError(..)"
#364967762 2019-12-17 05:37:19.355859641 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:19.553804053 UTC P2P Worker #1 WARN netapi block-propagation cannot message Global 35.230.2.230:3485: "SendError(..)"
#364967762 2019-12-17 05:37:19.590484103 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:19.638622014 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 35.233.0.162:3485: "SendError(..)"
#364967762 2019-12-17 05:37:19.642450809 UTC P2P Worker #0 WARN netapi block-propagation cannot message Global 34.85.92.6:3485: "SendError(..)"
#364967762 2019-12-17 05:37:19.685322323 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:20.593226243 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:20.685409734 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:21.548407383 UTC P2P Worker #3 WARN netapi block-propagation cannot message Global 35.230.2.230:3485: "SendError(..)"
#364967762 2019-12-17 05:37:21.595849899 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:21.614647820 UTC P2P Worker #0 WARN netapi block-propagation cannot message Global 35.233.0.162:3485: "SendError(..)"
#364967762 2019-12-17 05:37:21.641915189 UTC P2P Worker #3 WARN netapi block-propagation cannot message Global 34.85.31.119:3485: "SendError(..)"
#364967762 2019-12-17 05:37:21.685501929 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:22.059731325 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 34.85.92.6:3485: "SendError(..)"
#364967762 2019-12-17 05:37:22.357984173 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:22.598637390 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:22.685612250 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:23.086173404 UTC P2P Worker #1 WARN netapi block-propagation cannot message Global 34.85.31.119:3485: "SendError(..)"
#364967762 2019-12-17 05:37:23.211959453 UTC P2P Worker #3 WARN netapi block-propagation cannot message Global 35.230.2.230:3485: "SendError(..)"
#364967762 2019-12-17 05:37:23.420002722 UTC P2P Worker #1 WARN netapi block-propagation cannot message Global 34.85.92.6:3485: "SendError(..)"
#364967762 2019-12-17 05:37:23.601295048 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:23.641766807 UTC P2P Worker #3 WARN netapi block-propagation cannot message Global 35.233.0.162:3485: "SendError(..)"
#364967762 2019-12-17 05:37:23.685702369 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:24.604211465 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:24.685837824 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:25.183168256 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 35.230.2.230:3485: "SendError(..)"
#364967762 2019-12-17 05:37:25.344193384 UTC P2P Worker #1 WARN netapi block-propagation cannot message Global 34.85.31.119:3485: "SendError(..)"
#364967762 2019-12-17 05:37:25.359482897 UTC P2P Worker #0 WARN netapi block-propagation cannot message Global 35.233.0.162:3485: "SendError(..)"
#364967762 2019-12-17 05:37:25.361471308 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:25.391840906 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 34.85.92.6:3485: "SendError(..)"
#364967762 2019-12-17 05:37:25.606731117 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:25.685960279 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:26.609702715 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:26.686112553 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:26.860126470 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 34.85.92.6:3485: "SendError(..)"
#364967762 2019-12-17 05:37:26.861161222 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 34.85.31.119:3485: "SendError(..)"
#364967762 2019-12-17 05:37:26.929697545 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 35.230.2.230:3485: "SendError(..)"
#364967762 2019-12-17 05:37:26.937245993 UTC P2P Worker #2 WARN netapi block-propagation cannot message Global 35.233.0.162:3485: "SendError(..)"
#364967762 2019-12-17 05:37:27.612464839 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:27.686310331 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
#364967762 2019-12-17 05:37:28.364441429 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:28.615200476 UTC http.worker0 INFO rpc RPC call(chain_getBestBlockNumber([]))
#364967762 2019-12-17 05:37:28.658031061 UTC P2P Worker #0 WARN netapi block-propagation cannot message Global 34.85.31.119:3485: "SendError(..)"
#364967762 2019-12-17 05:37:28.686393587 UTC timer.worker.1 WARN netapi block-propagation cannot timeout 0: "SendError(..)"
```

該 issue 提供了執行時期日誌，顯示在區塊傳播期間反覆出現 SendError 訊息，但未指出任何原始檔、測試或進入點。首先定位區塊傳播警告，並追蹤失敗訊息和逾時處理；完成應意味著已確定原因，且重複錯誤已解決或得到適當處理。

由索引模型根據 Issue 內容生成。