About the #SaveShadowhunters campaign.
A QUICK SUMMARY
Shadowhunters is a TV show (imdb link) that got cancelled by FreeForm on the 5th of June 2018. The reason given to the fans of the show was that it got cancelled on "purely economic" grounds.
Fans of the show want it to be picked up again because of the importance of the series (especially the representation of POC and the LGBTQ+ community) and because the promised additional two hour special seems to be an impossible amount of time to tie up and give a satisfactory ending to the stories of all of the eight main characters.
Shadowhunters was poorly promoted by FreeForm for season 3 of the show, which also contributed to some of the anger.
Because of this, a lot of fans have taken to social media to protest the cancellation and in hopes of another network or streaming service to pick up the show. The main hashtag used is #SaveShadowhunters, but there is several others used depending on the day.