Reading Order Tool stopped working.

Hi! I am working on the reading order for a document and I have most of the document done but there are two sections of text that will not be picked up by the reading order tool. It goes like this--> I select the text with the tool, the text is highlighted with a purple rectangle, I click the type of content it is (in this case an H2 and some paragraph text) and then nothing happens. The reading order pop up box greys out, and the text that I had highlighted becomes un-highlighted, and nothing appears in the tag list. Essentially, like I never selected the text to begin with. I have almost the entire document done and it was working fine up until now. I have checked to make sure there aren't any empty tags (there aren't), I have restarted adobe, my computer, I tried on two different computers with the same document (same problem) so I'm guessing it's something with the document but I can't for the life of me figure out what. Any help is greatly appericated!