I've created a numbered list and a paragraph style for the numbered list. I'm using the same indent, negative first line indent, and tab for the whole thing, and it's set in the paragraph style also.
Everything works great until I reach the number 10 on the list, then for 10, 11 and all numbers after that, the next is indenting massively. I've looked at the Bullets and Numbering options for those specific lines and they look identical to everything else. I also have hidden characters turned on and I see nothing there to give me any clue as to why it's indenting. I have a picture just below it on it on the design so thought it might be a text wrapping thing, but deleted the photo and it changed nothing. I've searched online on all I see is issues with counterbalancing the first line indent with the left indent for numbered lists. Nothing on this happening to 2 digit numbers only in the numbered list.
When you option+click on the numbering button, it will bring up the dialog. If you have trouble getting this to work, show a screen shot so we can see what you have so far. Update the paragraph style after you make the edits.