I have had a number of experiences that make me wonder about this too. There is one explanation that made a little sense to me. Adyashanti is a teacher who talks a lot about the enlightenment process and what happens afterward as well. He says that it is a process most of the time rather than a one shot transformation. As one transforms the unenlightened parts of the self surge up to also be transformed - this can be an experience of the inner dark parts of yourself coming to light. Parts which were quietly repressed suddenly causing trouble because now the light starts to shine on them too.

Next here's where I extrapolate a bit.....if the outer is also a reflection of the inner then someone expanding their light would also attract outer darkness in the same way. That darkness too comes forward to either be transformed or interfere with the light in the person who is transforming. This could be anything from entities to the unenlightened parts inside of other people.