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Typically, I've mistakenly inserted some annotative leaders into a viewport modelspace instead of paperspace. Trying CHSPACE to bring them into PSpace makes them disappear - can't find them anywhere. Normal objects work fine.
You need to reset the annotative scale in modelspace to make them reappear: for a quick fix, you can set the annotative to 1:1 then back to whatever you are using.
Thanks for the reply, I checked my annotative settings and they did need updating as you suggest. Then I also realised I had Show Annotative objects-turned off -which wouldnt have helped really. All sorted! Thanks for the patience.