First, regarding the tweet you posted: It ignores the recent years. There are still local maximas in that graph. Second, it only concerns riots and leaves out any other type of violence. But that will be more clear upon how the author interprets 'riots'. It is just a graph without any explanation. Third, I could not find source of the data myself, as the graph is not from a peer reviewed journal so it can be easily discarded. Fourth, tweet is from a person who serves in the current government aka it is like Sarah Sanders, a vested interest always defending the government.

Communal violence under Modi has increased, even if it is a local maxima but their rhetoric is acerbic towards minorities and it shows. Now onto the communal violence sources:-

1. http://ksr.hkspublications.org/2016/07/27/the-rising-tide-of...

2. https://www.business-standard.com/article/current-affairs/co...

3. https://economictimes.indiatimes.com/news/politics-and-natio...

WhatsApp specific lynchings:

1. https://edition.cnn.com/2018/07/16/asia/india-whatsapp-lynch...

2. https://www.bloomberg.com/view/articles/2018-07-18/lynch-mob...

3. https://www.lowyinstitute.org/the-interpreter/india-dont-bla...