After you have completed a season in which you couldn't collect your Team Mission rewards, we invite you to sign a contract with another team or with the same team in a different step. Doing so will prevent the bugged Team Missions from being carried over to your next season.
Once you have signed a contract with a different team within the same step, you can complete the season or "give up" the season by tapping on the flag symbol above the list of GPs. If you then sign a contract again with the team with which you had Team Missions issues, you will be able to complete these missions and claim their rewards.
We hope this helps and we thank you for your understanding.