Sync fails with error "Unknown block header <n> <#node id> (Restart syncing)"

[chfast]

c4c… (Restart syncing)
INFO  02-08 12:08:01 p2p  sync   1235a5e2…|Parity/v1.11.8-stable-c754a02-20180725/x86_64-linux-gnu/rustc1.27.2 Starting full sync
WARN  02-08 12:08:01 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:03 p2p  sync   865a6325…|Parity-Ethereum/v2.2.9-stable-5d5b372-20190203/x86_64-linux-gnu/rustc1.31.1 Starting full sync
WARN  02-08 12:08:04 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:06 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Starting full sync
WARN  02-08 12:08:07 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:08 p2p  sync   865a6325…|Parity-Ethereum/v2.2.9-stable-5d5b372-20190203/x86_64-linux-gnu/rustc1.31.1 Starting full sync
WARN  02-08 12:08:09 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:13 p2p  sync   8ae105d7…|Parity/v1.10.6-unstable/x86_64-linux-gnu/rustc1.26.2 Starting full sync
WARN  02-08 12:08:14 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:15 p2p  sync   6a04d49d…|Parity/v1.11.7-stable-085035f-20180717/x86_64-linux-gnu/rustc1.27.1 Starting full sync
WARN  02-08 12:08:16 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:18 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Starting full sync
WARN  02-08 12:08:19 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:23 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Starting full sync
WARN  02-08 12:08:24 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
INFO  02-08 12:08:27 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Starting full sync
^CWARN  02-08 12:08:28 p2p  sync   5a4ab222…|Parity-Ethereum/v2.2.7-stable-b00a21f-20190115/x86_64-linux-gnu/rustc1.31.1 Unknown block header 58 #cd5b5c4c… (Restart syncing)
WARN  02-08 12:08:28 aleth warn   Cannot save network configuration while network is still running.

[halfalicious]

Is full logging enabled (-v4)?

[gumb0]

Which network was that? Could be expected, if it keeps connecting to the single node from another network

[chfast]

Mainnet. I think the faulty header was already in the database.

[fdouglis]

I am starting to play with aleth. I set up two instances on different VMs, but otherwise followed the example of creating a local chain -- instead of localhost and a new port, I point at the IP address of the mining host, and use the same port on both.

I hit the error reported here and found this page via a search. I see a comment that it could happen if connecting to one node, but no explanation why that would be expected. I turned on -v4 and got things like the following. Any suggestions?

DEBUG 02-04 21:40:09 p2p  blockhdr Expected trie root: 56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421
DEBUG 02-04 21:40:09 p2p  blockhdr Expected uncle hash: 1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347
TRACE 02-04 21:40:09 p2p  bq     Block #a96c66b1? is 2 parent is #c37894c1?
TRACE 02-04 21:40:09 p2p  bq     OK - queued as unknown parent: #c37894c1?
DEBUG 02-04 21:40:09 p2p  sync   0 imported OK, 0 with unknown parents, 0 with future timestamps, 0 already known received.
DEBUG 02-04 21:40:09 p2p  sync   Already known or future time & unknown parent or unknown parent, block #2. Resetting `sync.

Thanks.

[fdouglis]

I'll add that I think I've gotten around this by removing ~/.ethereum on the non-mining host and restarting aleth with no existing chain. It seems happier now.