Having the same problem- cant backup manually or automatically above 1GB, and also cant restore a course above 1.6GB, and nobody seems to have worked on a fix for 2.5 and below (as far as I have seen, hopefully im mistaken)- all efforts seem to have been concentrated on making sure 2.6 can handle them.
looks like im going to have to do an early upgrade antd try and make 2.6 look identical to 2.5.... hoping i can turn off the new activity chooser...