Difficult to describe this problem but in one particular document I am working on (a book), whenever I place the cursor near any of the margins, a glyph or icon with two straight lines and an arrow below and above, pointing opposite directions, appears and makes it impossible to move the cursor to that point of the text because instead it wants me to move the margin.

Is there a way to turn off this function? I am at a loss since I don't even know what words to describe this glitch, and so cannot search for it online

thanks in advance