some checkpoint values cause failed syncs

[ncitron]

Using 0x85e6151a246e8fdba36db27a0c7678a575346272fe978c9281e13a8b26cdfa68 for example causes an RpcError on fetching the bootstrap, immediately followed by an InvalidPeriod error. It seems other checkpoints in this sync period are failing as well.

[malefooo]

I changed a block root to try, the query is always this, very confusing
Is there any requirement for this block root? Can't you just assign one?

{
  "code": 404,
  "message": "LC bootstrap unavailable"
}

[ncitron]

So there are only certain slots that will work. They need to be the first slot in an epoch. There does seem to be an additional issue with certain blocks, which is what I want to investigate with this issue.