Ed Decter, the showrunner for SHADOWHUNTERS season 1, has apparently left the show suddenly, with no word on why.
According to Deadline, Shadowhunters showrunner and series creator Ed Decter has left the series prior to the production of season 2. It was heard that he has left due to creative differences, and because of his sudden departure, there are no word on any replacements for him as of yet.

I hear Decter departed a few days ago and was not present at today’s first table read for Shadowhunters‘ second season. I hear the departure was over creative differences, and the new showrunner(s) are expected to tweak the series’ creative direction for Season 2. In the meanwhile, production is expected to continue as scheduled, with no impact from Decter’s exit.
Farewell Shadow World! The @ShadowhuntersWR, cast and crew the finest I have ever worked with! Love to our SH FANS, best on earth!
— Ed Decter (@EDecter) August 5, 2016
Despite Decter’s departure, it doesn’t seem there will be any major issues with the development of the series for season 2, and production will likely go on as scheduled.
Regardless of what was reported, there hasn’t been any official word as to why Ed Decter left. We do believe he truly loved the series, and was excited with what he had planned for season 2. We may never know about his plans now, but as a fandom, we still have faith the series will be able to stand strong. We can only hope Freeform finds someone who loves the Shadowhunters series and books as much as we do.
Shadowhunters season 2 is scheduled to premiere sometime early 2017.