We have been continuously facing indexing issues for a few customers for the last two weeks. Google is indexing some pages and dropping some pages whereas sites are fully optimized having original content and have all pages indexed earlier.
We tested the Google search console and found a few pages not indexed and requested for indexing and got it indexed in 4 days. These were old pages that were duly indexed earlier and instantly dropped out of the Google index.
The matter is already reported by Barry Schwartz on SE Round Table and there are numerous complaints and reports on google dropping In and Out of the index. All sizes of websites Big, medium, and small are affected by this change.
John Mueller from Google is also not aware of the issue and when asked he said to pass it on to the technical team.