[caplin] beacon API /eth/v1/beacon/headers/ sometimes 404 when queried by slot number

[wmitsuda]

using e3 main:

see the following example on my sepolia node, first I queried the head slot. it returns the slot 6020295.

then I explicitly query slot 6020295, it returns http 404.

http <my-node>/eth/v1/beacon/headers/head
HTTP/1.1 200 OK
Content-Length: 688
Content-Type: application/json
Date: Thu, 03 Oct 2024 18:05:47 GMT
Vary: Origin

{
    "data": {
        "canonical": false,
        "header": {
            "message": {
                "body_root": "0xe1a8238373d71bd6bf94b9f4b3e2c123aaa942d41de64cc2e61547bbc61f0cb7",
                "parent_root": "0xc6fd3191a64eb2ffd5716b7014f3bfcfc98a360129047254a8a25941f494e8ab",
                "proposer_index": "845",
                "slot": "6020295",
                "state_root": "0x969920df53487be7f9eb067e8aee3907d05ae8684f20cba6516e3c6b1173a2d7"
            },
            "signature": "0x95adbd5f4a3493936e7f7ebad9cf46de5b4afa350f31c67eb1ca8818422c2d91f1d461c95ba39689d19cd2b3f1337d1d05e2d45f9180ea74fe
ad954cb1492503ff1c781dcfafc2c25cbeed932fa403857fb59fd5b90994b36273795d9e86eb6a"
        },
        "root": "0xda903f64213c2e60a683a9cb80c102dfb22475e08ab345a923b88d6e673de54b"
    },
    "execution_optimistic": false,
    "finalized": false,
    "version": "deneb"
}

http <my-node>/eth/v1/beacon/headers/6020295
HTTP/1.1 404 Not Found
Content-Length: 49
Content-Type: text/plain; charset=utf-8
Date: Thu, 03 Oct 2024 18:05:54 GMT
Vary: Origin

{
    "code": 404,
    "message": "block not found 6020295"
}