Getting the Skin Diver and Channel Crosser at the same time is the correct behavior.
On the 11th day of logging in (your 10th day of logging in two days in a row) you’ll get the first Skin Diver and be ⅓ complete on the Channel Crosser.
On the 21st day of logging in you’ll get the second Skin Diver and be ⅔ complete on the Channel Crosser.
On the 31st day of logging in you’ll get the third Skin Diver and receive your Channel Crosser award.
We’ve always had a rare bug that caused duplicates of things from time to time but it’s been very rare up until this incident. I assure you the second we can reproduce it and figure out what’s going on we’ll fix it.