My last DH French Vanilla cakes also broke horribly all around the edges when I tried to get them out of the pans. They were 10" hearts and I used CC's cake release as well as wax paper in the bottom of the pans. Ended up making cake spackle and everything looked fine in the end after covering with fondant, but that's not the sort of thing I like to do.

check the use by date on the box maybe the mix is outdated

I always use DH and have not had a problem with rising or sinking!!
thank goodness....never had to stray away...