YouTube Data API does not return live videos for specific channel

I've had a server side script for quite a while that periodically polls the YouTube data API to check for any current live streams to display them on a website. This script has been working perfectly fine for over a year until recently it's stopped working.

The script is a basic server side cURL request that has the following query:

https://www.googleapis.com/youtube/v3/search?
    key=<API KEY>&
    part=snippet&
    channelId=UCKBI1GR0if65sto7PRV5drw&
    eventType=live&
    type=video

This channel in particular always has at least one live stream running, so I can always expect it to return a result. However as of a few days ago, the response has been the following:

{
  "kind": "youtube#searchListResponse",
  "etag": "\"xwzn9fn_LczrfK9QS3iZcGzqRGs/Yv4Uk7SrgMahOJF6jlPF1ppvsbc\"",
  "regionCode": "AU",
  "pageInfo": {
    "totalResults": 0,
    "resultsPerPage": 5
  },
  "items": []
}

Nothing to the query has changed on the server side. What makes it even more peculiar is that if I substitute the channelId with that of another channel that has a live broadcast, I am able to return results. This rules out any quota limits on the API being exceeded or the validity of the API key itself.

Similarly, if I change the eventType parameter in the query from live to completed, I can see results appear for the channel. It seems to be an issue with querying only live events.

I've seen in the past in a few other questions that this may be a recurring issue with the data API, such as this question. However this was about 6 months ago and the issue seemed to affect more people than just myself.

If someone could point me into the right direction, wether there may be an issue with the channel itself or something with the API that I'm missing, it would be greatly appreciated. Thanks in advance!