FAQ

This is explained in a flashback. To sum it up, Salazar was mercilessly hunting down pirates, Jack took command of The Black Pearl (at the time called "The Wicked Wench") towards the Devil's Triangle, with Salazar giving chase. Jack outmaneuvers Salazar, causing his ship to get trapped in the Triangle, which leads to him and his entire crew being killed, trapped and cursed within. So naturally he's a little unhappy with Jack, as most cursed sailors seem to be.

Jack had given the compass to Elizabeth, Will and Gibbs at different times in the film series. However, he only loaned it to them, he did not actually give it away in exchange for something else. In this film, Jack "betrays" the compass by trading it for a bottle of rum. Therefore transferring ownership to someone else. This released Jack's worst fear; Salazar.

In Dead Man's Chest, Tia Dalma says to Jack "The compass you bartered from me can't lead you to [the chest]?". However in this film, the flashback shows that Jack received the compass from the previous captain of the Wicked Wench right before his death. It's likely the filmmakers just chose to retcon the origin. But it could possibly be said that Tia Dalma once stole the compass from Jack and so he had to barter to get it back from her. As Jack implies the two have a complicated history.

It was established that because Davy Jones stopped ferrying the souls of those who died at sea, this caused Jones and his crew to become corrupted and fishy. However, the beginning of this film has Henry, at 12 years old, locating the Dutchman. The ship and Will have taken on the fishy look once more, though significantly less so than Jones. It's possible, due to Davy Jones not doing the job for so long, there was such a back-log of souls to be ferried, that Will simply hadn't been able to catch up yet. So he began to take on the fishy appearance.

He was most likely in the afterlife, ferrying souls for the majority of events in the film.