South can often fail for reasons that are surprisingly silly, at least in my experience. Though it's still pretty useful compared to having nothing.
In the latest version(beta?) you can actually have a column with 'default current_timestamp' and a column with 'on update current_timestamp' in the same table after years of only being able to have 1 column per table auto that way.
I don't remember the details, but I think I had to fill a column with zeros all the way down just to drop the whole column in the migration anyway or something along those lines.