I have a Dracaena marginata that I've had for a few years now. I moved it to a new location about a year ago - with the only noticeable difference being that it's a lower-light environment.
Similarly, for the last year or so, I've noticed that it's been dropping a fair number of leaves in a progression similar to the attached image. Usually a few dark spots appear somewhere in the middle of the leaf, and then the entire section turns limp and brown, before the leaf completely dies.
Is this related to moving the plant to a lower-light location, or is there something else happening? There continues to be new growth, but the plant looks sparser than I recall...