I got a tough one for you and not only because it's probably rather unknown - I also barely remember anything.

What I do remember is that it's either in a church or in a school (or not), it's about some people that research a weird energy (or not) and that there was a scene where one or more homeless people or zombies that stand in front of a building in a yard and they get eaten or turn into alot of insects. I think there was also a scene where a woman gets drawn into a mirror.
So yeah, that's all I remember, most of it extremely vague, only that it really scared me when I was a kid. I think it must have been a movie from the 80s, but not sure.

Good luck! :D