Why could Youtube API stop working?

Question

YouTube

Hello.
This morning I started receiving empty responses to Youtube API requests, which had previously worked fine for three months.
Request example: getting a list of videos from a specific Youtube channel. Channel ID: UCwHnsUEYrQUTUxC4dvrv0QQ
Request code:

GET https://www.googleapis.com/youtube/v3/search?part=snippet%2Cid&channelId=UCwHnsUEYrQUTUxC4dvrv0QQ&key={YOUR_API_KEY}

Query result:

{
 "kind": "youtube#searchListResponse",
 "etag": "\"gMjDJfS6nsym0T-NKCXALC_u_rM/Z7muB3yLsIIdSeQTKlRVObzSk8M\"",
 "pageInfo": {
  "totalResults": 0,
  "resultsPerPage": 5
 },
 "items": [
 ]
}

The real state of affairs: in channel 4 videos.