Swim Interval Zones Way Off

I am a new user to intervals, and cant figure out what I am doing wrong with my swim zones. Yesterday, I filled in my Critical Swim Speed (1:21) and took the autofilled zone suggestions and applied them to my swim workouts. Now it is showing almost all of my swimming as zone 7, even as slow as a 1:38 pace, which should be zone 1 or 2 according to my zone chart in settings. See screenshots below. Would love anyone who can point out what I did wrong.

Figured it out I think. I updated my threshold pace after this activity (this was my test), so it used the default pace of 2:00 for this activity. When I swam today, my zones are correct.

New question - is it possible to apply the new zones to activities which took place in the past?

Click the “Update Activities” box in /settings for the sport to apply the zones:

You can also do this for selected activities in the activity list view:

I just did this both ways, and for some reason it didnt work. It is still showing Z7 for all my easy stuff. It is not a huge deal since I have only done like 4 swims, but weird that it wont work.

I spotted the problem. Your threshold pace on some of your swims is 1:50/100y instead of 1:21/100y. You can just click it to edit.

perfect, thanks!