YouTube Data API playlistItems:List only returns max of 100 data items - or 2 pages of data, was working normally July 16

I am using YouTube Data API v3 – and today playlistItems:List only returns max of 100 data items or 2 pages of data for the all videos playlist (UU + last 22 char of channel id) . I believe the next page token also may be incorrect after the first page, because it shows the wrong previous page token on the third page.

UPDATE: Further testing shows that the playlistItems:List api works correctly 
for some channels -

All video playlist - UU4mLlRa_dezwvytudo9s1sw works

https://developers.google.com/youtube/v3/docs/playlistItems/list?apix=true&apix_params=%7B%22part%22%3A%5B%22id%2Csnippet%22%5D%2C%22maxResults%22%3A50%2C%22playlistId%22%3A%22UU4mLlRa_dezwvytudo9s1sw%22%7D


but at least two others do not work correctly and only return 100 items:

UUGGZ_POGmIWG1pQXTDzQv-g
UUwD4x63A9KC7Si2RuSfg-SA

This has been working correctly for several years. It worked correctly July 16. The same behavior happens in the API Explorer.

API Explorer example & results for all video playlist UUwD4x63A9KC7Si2RuSfg-SA:

https://developers.google.com/youtube/v3/docs/playlistItems/list?apix=true&apix_params=%7B%22part%22%3A%5B%22id%2Csnippet%22%5D%2C%22maxResults%22%3A50%2C%22pageToken%22%3A%22CDIQAA%22%2C%22playlistId%22%3A%22UUwD4x63A9KC7Si2RuSfg-SA%22%7D

first page of results:

{
  "kind": "youtube#playlistItemListResponse",
  "etag": "oE9yCl2NBCpgzQbX82RR1jjqkco",
  "nextPageToken": "CDIQAA",
  "items": [


second page - page token CDIQAA:

{
  "kind": "youtube#playlistItemListResponse",
  "etag": "w8PJ0yDadTWJfwSP2CWcODoMzuk",
  "nextPageToken": "CGQQAA",
  "prevPageToken": "CDIQAQ",
  "items": [

third page - page token CGQQAA:

{
  "kind": "youtube#playlistItemListResponse",
  "etag": "AQSyYYKWgu50RiGPA10TjRTE7Ys",
  "nextPageToken": "CJYBEAA",
  "prevPageToken": "CGQQAQ",    
  "items": [],                  <---- NO DATA, but 521 items still to show
  "pageInfo": {
    "totalResults": 621,
    "resultsPerPage": 50
  }
}

POSSIBLE WORKAROUNDS

1. Use YouTube Data API v3 – search:List specifying channel ID, no query, and result filter type = videos. This is expensive in quota, it costs 100 quota per query/page of 50 results. However, this API now seems to max out at about 300 or so results for a channel.

2. Use YouTube Data API v3 – playlistItems:List with a channel-owner authorized OAuth token instead of the public API key. This works as before without the 100 item limit. However, it means you cannot get a video list (over 100 videos) for a channel or a playlist without an OAuth token from the owner.