I'm having a problem with the autmatic numbering of figures in a document. It may have been caused by copying and pasting captioned/numbered figures from another document. The first figure already has a caption on the preceeding page which says Figure 1 but I wanted to label it on the page where it's present; this says Figure 2, however. If I try to make a new caption for this figure, it's referred to as Figure 4?!

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Caption numbers are SEQ fields. The quickest way to figure out what is going on is to toggle display of fields (Alt+F9).

Insert a Caption - Complex Documents

Here is more on the SEQuence Field. The idea is to make them all use the same identifier.

Here is Microsoft's help file: https://support.office.com/en-us/article/field-codes-seq-sequence-field-062a387b-dfc9-4ef8-8235-29ee113d59be?ui=en-US&rs=en-US&ad=US

You may also have an abandoned caption underneath one of your images. Try editing in draft view.