Investigate odd lighthouse error during catch up sync

[dboreham]

We keep seeing this error in the lighthouse logs after a warm restart:

WARN Error whilst processing payload status  error: Api { error: Reqwest(reqwest::Error { kind: Request, url: Url { scheme: "http", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("mainnet-eth-geth-1")), port: Some(8551), path: "/", query: None, fragment: None }, source: TimedOut }) }, service: exec

Evidence suggests it is not as simple as a timeout on a request to the sibling geth (geth seems perfectly happy).

[dboreham]

Perhaps relevant that this message seems to only be seen when lighthouse is not synced up to head:

INFO Syncing                                 est_time: --, distance: 58 slots (11 mins), peers: 17, service: slot_notifier

[dboreham]

Actually since the slot backlog count keeps increasing, it may be that sync is totally stalled. Perhaps the stalled sync and the message about whilst etc are related.

[dboreham]

Suspicions supported by the fact that after a stack restart the errors do not reappear.
Theory is that lighthouse put itself in some bad perpetual stuck state.