This reply that I recently posted for someone relates to a much younger child, but I think in principle it may be relevant to your child also:
QUOTE
I always answer this kind of problem, by suggesting that as a baby matures, becomes more aware of 'self' and their environment, things that previously they ignored or were not aware of, start to take on a more 'dangerous' or threatening image in their 'little world'.
Over the years (and you ARE in it for the 'long haul', maybe thirty years or more!) there will be VERY MANY changes that will occur, that are just 'phases' or inexplicable happenings, that you just have to cope with.
As in all things child-related, as much as possible, try to AVOID places and situations that will trigger unhappy reactions, or might tempt unwanted behaviours.
UNQUOTE
You seem to have been doing well up until now, so it sounds like most of your strategies have been OK.
Personally, I would try to avoid 'night lights' and similar things, as a child does need to get used to a fairly dark environment; just have a glow from under the door, or something similar, so it is not TOTAL darkness. Shadows, or patterns on curtains or wallpaper can take on strange shapes, which a toddler's developing imagination may interpret as scary or sinister. So things a baby would not notice, may start to seem important to an older child.
So, be as reassuring and supportive as possible, and before too long things should improve.