Hmm... not sure about this, but I do see one GIF and one PNG in the output list (in addition to all the TIFFs).
Try this: With absolutely nothing selected, set the desired default image output type (e.g. GIF) in the Optimize panel.
If that doesn't work, then select all (Command-A), and do the same.
Good call! That seems to have the same effect as deselecting all objects on the canvas and then choosing a format in the Optimize panel. (I don't know if it's necessary to do that for every page or not, but it certainly couldn't hurt.)
Just know that you can also override that general setting by selecting an individual element (like a slice) and applying a new setting to it via the Optimize panel.
Europe, Middle East and Africa