Messages seem to disappear from /message/tx_seq_num

It seems messages are disappearing from the API and are not retrievable after a certain period of time. Is that the case?
Right now, the latest message beamed is #392 so `https://api.blockstream.space/message/392` returns a message, but #393 returns
```
{
"message": "Sequence number not found",
"errors": [
{
"title": "Sequence number not found",
"detail": "Sent order with that tx sequence number not found",
"code": 114
}
]
}
```
and all messages before and including #314 return a `HTTP 404 Not Found`.

Also, please note the discrepancy between message numbers that "have been" and the ones that "haven't been yet".