elos42, your graph essentially corresponds in time period to the largest series of reporting bugs I can ever remember seeing on Google, which resulted in a series of threads.
That said, though, the reported bugs were about pages dropping out of the reported index, whereas your graph is showing upswings. I don't know whether there's a connection, and whether the threads will help you work out what was actually happening.
This thread noted below is more or less the beginning of the bugs... Some were reporting errors, but I'm not sure about all of them. I tried to keep the threads linked to subsequent and related thread(s) as new bugs were identified by Google...
Reports of Google Dropping Pages Out of Index... possibly a bug? April 5, 2019 https://www.webmasterworld.com/google/4941198.htm [webmasterworld.com]
Note that the threads were probably slightly behind the changes, as it took a while for posters here to notice that changes were continuing. Vital in all this reporting, I should add, are Barry Schwartz's seroundtable articles, which I reference in our threads.
I should note also that all this was preceded by changes and limitations in the Google Fetch (to index) Tool, as Google was trying to prevent use of the tool by spammers and those who wanted to maintain fresh listings. You mentioned that you're a news site, so you might have used the Fetch tools as a submission tool, and/or many other news sites might have done so. Conceivably, if competitors lost traffic for a while because Google wasn't indexing them, you might have gained.
Big reductions in crawl-to-index limits on Google Fetch tool March, 2018 https://www.webmasterworld.com/google/4893740.htm [webmasterworld.com]
This may or may not apply to you... and again, you'll have to piece the competitive picture together. Please keep us posted on how you think this might have related to what you saw, as artifacts from the Fetch Tool update and the reporting errors are otherwise hard to track.
There have also been big changes made in the news algorithm, I understand, with originality and freshness counting for more than previously... so if you're using off the web sources (ie, effectively adding original content), this might account for the upswing you're beginning to see. And nine months or so is not an unreasonable amount of time for it to have taken this long. I encourage you to continue what you've been doing, as your graph does seem to have started another upward movement, as you note.
Hoping this helps.