I saw the change when I switched my outlook from a sunday to saturday week to a monday to sunday week. I do not know if leap day was part of the issue. When I login to to teams online, the appointments are on the correct date when I use work week or week (cannot customize to monday-saturday).
On my laptop, I'm using old teams and the meetings are a day "ahead" mondays meetings showing on tuesday, etc. the desktop application is showing week but saturday and sunday are not appearing. When I change the teams view to "work week" the meetings appear on the correct days.