It seems to have had stable unique views up until Aug-Sep 18 [1]. At some point it suffered from country-wide bans in places such as Indonesia. The country bans coupled with a ban from the iOS App store [2] caused direct downward pressure on viwership. This has led to a rapid drop in viewership in the months after [3]. Considering the amount of legislation towards telecom companies and the potential risk to the Verizon brand by proxy, it was imperative that the company would sell Tumblr.
Due to the current political environment in the US, it is unlikely that Automattic will open the gates that partially made Tumblr what it was in the 17-18 era for the next 3-6 months, that is unless they take a very conservative take on reviewing that kind of content prior to it being posted.
[1] [3] https://www.statista.com/statistics/261925/unique-visitors-t... [2] https://www.theverge.com/2018/11/17/18100156/tumblr-apple-ap...