I experience something like this in spontaneous conversation. One of the reasons I have trouble with order is I always seem get the feeling that I need to explain what im talking about or why, which causes me to "jump around" even from mid sentence. Also I'm constantly associating items of the conversation to memories (usually autobiographical) which a lot of times causes me to derail into tangents; having sensory problems only adds to this. If someone happens to ask me what my plans are for any given day, it usually comes out unsorted and a bit jumbled.
It would be hard to say what single thing causes this; it maybe the way we access our memory, or form associations with it? Recently I've been trying take my time with questions instead of trying to answer immediately (in essence it seems like it should help overall lol). Its also easy to mix things up if something else is on you're mind (a book, something someone said, special interests, ect), so in that situation being mindful enough to temporarily discard a preoccupation could be helpful as well.
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