Yes, as CyberAngel said ML1 very well could be an annotative ghost image of either one of the other leaders but is not visible because it is a different annotative scale than ML2 and ML3.
Make sure the sys variable SELECTIONANNODISPLAY is set to zero. That one can drive people bananas on skates. If the variable = 1, then upon selection, ALL the ghost images of selected annotative objects suddenly appear.
You can also set ANNOALLVISIBLE to 1 so you can see the wayward critter(s) all the time. If you didn't start this drawing and you are not familiar with annotative scaling, this will be fun. LOL
Without ANNOALLVISIBLE = 1, you wont be able to select ML1 unless the current annotative scale in the space you are working matches that of the invisible object. look for it in modelspace because you don't want to change your anno scale in a viewport. If it = 1 then you can select and edit the other annotatively scaled objects.
Without doing all that, you can select ML2 and click on ADD DELETE SCALES to the far right of the Annotation ribbon. That will tell you which, if any annotative scales are assigned to ML2 and 3, and allow you to get rid of the extra ones if not needed. If this is not your drawing you may not want to do this because it may disappear the leader in a viewport where it is needed.