Why are there mixed opinions on reversal of nissen fundoplication surgery? is reversal safe, difficult?

Safe: It can be safe, but always risks with any surgery. Find someone who is an expert in the field, does a lot of laparoscopic stomach surgery and they will do a good job for you. It isn't difficult to do, except for some surgeons- so find the ones who do a lot.

It is more difficult: To undo a nissen fundoplcation than to do it. After creating a nissen fundoplcation, it gets really scarred in place. To take it down puts the distal esophagus and gastric fundus at risk for injury. The only reason to consider taking one down is intolerable gastric bloating with inability to burp or vomit afterwards. And you have to consider why the fundoplcation was done in the first place.