Calendar app icon is changed to tasks app icon
Problem: When enabling the tasks app icon or whenever the app is updated, the first aCalendar app icon added to your home screen will change to the tasks app icon.
Status: This is a bug in Samsung's One UI 2 launcher. We have already informed Samsung about this and we are hoping for a bug fix soon.
Workaround: You can avoid this issue by moving the (first added) aCalendar calendar app icon to a page at the far right of your home screen and add another app icon to your primary home screen. Alternatively (in case you don't need the tasks app icon), simply deactivate the tasks app icon under settings - tasks.