Do you see the dashed line around the collection? That indicates it's a group, and the group is anchored. The easiest way to deal with this, in my opinion, if you need to add to the group is to do it with the Layers panel. Put the image/text where you want it, then open the alyers panel and drag it down into the group (you'll probably need to select the group so you can identify it in the panel, but new stuff should be at the top of the stack).
In the photo up top, the EXD 11-12 DE is the object that's not anchored (I had already put it into the spot I want it), when I drag it into that group, this happens:
It creates a whole bunch of white space, moves the parts I wanted down farther, then pushes all the original info over in between both pages. Any idea why?
It's probably to do with the anchor settings, but I'd need to see the file to figure it out.
You can also try releasing the anchored group, ungrouping, then select all the objects and regroup, then re-anchor, but that's a lot more work.
I got it! When I dragged it into the group, I right clicked on it, and selected "Select and Fit item" then I was able to move it around freely, and moving it over corrected all the others.
Thanks for your help!