When calling `newPayload` on a >1MB payload (can happen post-merge),
`news` splits up that payload into 1MB chunks. The chunks are each sent
individually, though, with `await` in-between. This means that when we
send concurrent `forkChoiceUpdated` calls, that those may end up getting
in-between the `newPayload` chunks, leading to invalid data being sent.
The EL then returns an error message with a `null` `id` entry (as it
could not read the request `id` due to the mangling) and disconnects.
A PR has been submitted to fix this in `news`, and merged into `status`
branch early as this fix is critical for reliable post-merge operation:
https://github.com/Tormund/news/pull/22
ebfb624557