Trades now have changed and instead of 6 tasks refreshing every 24 hours, we get 3 tasks that refresh every 12 hours. There is also a progress bar in the trade window showing you the next set of rewards.

This progress bar will show completion for the next available reward and will stay there till completed. So nothing to worry over if you see that you need to complete 4 tasks but you only have 3 available before the next refresh.

Refresh functionality affects the tasks available, not the rewards. Those will be there for you to claim them as soon as you complete the amount of Trade tasks needed.