Cameron was emailing rewrites straight to set throughout the shoot, in lieu of his usual practice of handing cast members his rewrites before yelling action himself.

Miller has also described having to film at least one scene he didn't want at all, along with a bunch of comedy stuff Cameron insisted on (though most of that got cut later). The crashing plane, the stuff about Dani being Grace’s foster mom, and Arnie's involvement were all Cameron, and Miller's preferred version of the Future War was vetoed by Cameron.

That's why the movie has a slightly schizophrenic feel. Miller had more control over the first half than the second one.