There were rumours that Warner Bros. produced two edits of Suicide Squad. The first was supervised by David Ayers, the director. The second was done by the company who put together the Bohemian Rhapsody and Ballroom Blitz trailers, and was the one shown in cinemas.
Ayers's cut is supposed to be a bit darker and more sombre. Maybe it'll turn up on a DVD at some point.
There's not necessarily a problem with reshoots. Fury Road apparently had a fair amount done, and that turned out OK. Extensive reworking of a film might indicate issues, especially when there's studio interference. Rogue One is rumoured to be a victim of this.
I think that Dylan's right when he brings up limited preparation time. These movies tend to have a date announced before production begins, and often an aggressive schedule.
I went to see League of Gods today, which is a strange, Chinese Kung Fu fantasy film. I'm not sure it really made that much sense, but it looks pretty.