Summary:

After hiding an IG comment via the API, the comment cannot be retrieved via GET without receiving an "unknown error". Unhiding the comment makes it available to GET requests again.

Posting here because bug reporting is apparently disabled?

To replicate:

A) GET comment without issue: /18042700435917780?fields=hidden

{
  "hidden": false,
  "id": "18042700435917780"
}

B) POST to hide comment 18042700435917780?hide=true

{
  "success": true
}

C) GET the same comment, unknown error occurred 18042700435917780?fields=hidden

{
  "error": {
    "code": 1,
    "message": "An unknown error occurred"
  }
}

Though not required for replication, the comment can be unhidden via POST with ?hide=false which results in the comment being available via GET reqs again.