It has been confirmed by a Google spokesperson that Google has not pushed out a new core search update and no infrastructure changes were pushed out around the March 2019 core update or the more recent de-indexing bugs that happened last month.
The last core update to be pushed was that March 2019 core update and Google has not released another since –even though there being rumors there may have been an update afterward.
You can learn more about when Google does updates in this Twitter thread:
Is it possible that these fluctuations are a result of the new evergreen GoogleBot released last week? More than likely not. According to Google, this new GoogleBot was released over several months and it was actually being used for 10% of crawling back in November. Google also said the indexing bugs and the new GoogleBot are completely unrelated.