Aquaman felt like two movies running at the same time. One was a fun action comedy, the other was a serious movie that had places to go. Each scene had plot shots and comedy shots, and they didn't feel like they had been shot together.

My theory, based on zero research, is that half the movie was reshoots. Whether it was shot super serious and turned into a comedy later or the whole story was replaced after the fact, I don't know. Either way, it likely bears little resemblance to what he walked on set for.