Have same issue, found secret passage with candle room, but how to get candle there? it's too high to reach it and don't have feather to fly. Ok sorted it out:)
But stuck anyway after collected third letter in room with dissapering platforms. Next item is in shape of diamond around in room blocked in left corner.
Ok, collected that item, but it's not a key item, and can't progress further. Checked all rooms in game, and need to exit it as there is no any visible way to progress further. Thanks to developer for cool game, but without my saved progress, doubt that going to try it again, sorry.