HappenStance causes WSoD?

I’ve been using HS theme since 2015. A few days ago I tried to log in to the webpage and I saw white screen of death. I didn’t change anything on the webpage I didn’t install new plugins. All plugins an WP were up to date. I started to disable plugins via FTP, but nothing happened, so I activated plugins again. When I disabled theme, I saw a login page. I changed the theme and everything works perfect on the new theme. What happend?