Google, giant search engine and career for search engine professionals, sometimes its a nightmare to them because of the unexpected twists Google announce as updates.
Google launched that they are running a Broad Core Algorithm in March 2018 and it is still running, as Google conducts multiple times in a year. Some are very widespread changes, and you won't set it if it goes right out wrong.
They bluntly warned that they will not fix if you do something wrong in that process, so you should be careful with that point because competition is really very heavy and mistakes will not be tolerated.
If you are waiting since long time for your web page rank improvement (though you are working sincerely) then you can gain some rank (not applicable to all).
In Google official Twitter page some are crying like "my site has dropped down, what i have to go now"
You have to focus on content, and wait for your turn.
So the idea is, we have see things in much broader way and do market research regularly, it helps.