Dear Owen_627,
Good! hope you are doing well.
I truly appreciate your effort and the valuable time you took to respond. First, please accept my apologies for the inconvenience you have encountered. I understand the impact this issue has on your daily work.
I would like to summarize this issue to make the information easily accessible. This will also help other community members find solutions more easily if they come across the same situation.
Issue Description:
Planner error message - We couldn't complete your request because your item or storage limit has been exceeded
Environment:
Office 365 for business.
Microsoft Planner
Suggestion:
Split the plan by moving some of the tasks to a newly created plan and we also encourage you to share your thoughts and suggestions through our feedback community under Planner · Community (microsoft.com). To let the product development team know your needs and help improve our products and services.
Meanwhile, if you can understand my explanation and correct direction information about this entire scenario, I would like to request you to provide a valuable vote in above mentioned reply so that other users can understand the whole situation.
Have a nice day and stay safe 😊
Sincerely,
Ralph Chawatama | Microsoft Community Moderator