A Google indexing bug caused some pages to be removed. The indexing problem could be seen in the number of pages that appeared in the index report in Search Console and also when using the site: command (which retrieves only pages from a particular domain).
The only solution at this point was to request the re-indexing of a single page. The fact google did not allow re-indexing requests for multiple pages, was a significant problem for some web owners who "lost" almost 50% of their pages.
Three days later (on April 7th) Google announced the problem was fixed, but soon changed the announcement, saying the problem was not completely repaired. John Muller added that anyone who is not sure whether his page is indexed or not can also use the Search Console’s URL Inspection Tool.
The last message from Google came on April 10th, when it announced that the problem had been completely resolved, but did not add further details or explain exactly what the problem was.
Losing information on Search Console
Although the bug itself has been fixed, it appears that all the Google index data collected between the 5th and the 25Th in various Search Console reports was not shown. Instead of the correct data, the previous wrong data continued to appear, creating a straight line on all graphs, except for the performance reports that measures search results appearance. Therefore, it is not possible to know whether your site has been influenced by this bug strictly by checking your Search Console account.
What to do if you were damaged?
Fortunately, the indexing problem appears to have been a “one-time event”, with the exception of two more “one-time events” in May, similar problems were not reported. If you have seen an unexpected fall in the number of users at this time of the month, the problem is probably not yours to handle, and was not caused due to a particular action you have taken.