Lodestar produces blocks with empty sync aggregate

This behavior has been observed on the [Mekong testnet](https://mekong.ethpandaops.io/).

Eg. https://dora.mekong.ethpandaops.io/slot/274010 contains an empty sync aggregate (0% participation)

There are no obvious error logs that could explain this, the only log (from `lodestar-geth-3`) I found was from our light client server which was complaining about it
```
Dec-13 17:22:00.136[chain] debug: sync committee below required MIN_SYNC_COMMITTEE_PARTICIPANTS syncPeriod=33, attestedPeriod=33, syncAggregateParticipation=0
```

This seems to be isolated to electra / mekong / devnet-4 where it can be observed quite frequently, also has been reported by [Luca on discord](https://discord.com/channels/593655374469660673/743858262864167062/1314287158395277404).