I'm experiencing a problem with the Windows app for Teams that is new behavior in the past couple of months. When I create a team and go to attach a Plan to it, I no longer have an option to use an existing plan. All I can do now is to create a new plan.
I just tried again this morning, using both the Teams app and from teams.office.com.
This is a problem mostly because of a bug I and others on my team experience where tasks entered in a Plan view from within Teams are invisible to the Plan view when accessed directly from Planner (either from the iPhone app or from tasks.office.com). A Plan instance created from within Teams does show up in Planner, but it doesn’t show any tasks or buckets added to the Planner view from within Teams. Add something to that plan from within Planner, and it doesn’t sync with the Planner view from within Teams.
It used to be you could get around this synchronization problem by creating the plan within Planner and then when you go to add a Plann instance within Teams, there was an option to add an existing plan to the team. This workaround allowed plan views within Planner and Teams to stay in sync. Now, all I can do is create a new plan for the team, and anyone used to working directly in Planner now has to work in the plan view within Teams. The latter view within Teams used to be terrible, but it seems fully featured now.
So, to use Planner now, I’m just creating plans within Teams and dealing with this deficiency. It’s not good.
Meanwhile, if you use the My Tasks view in Planner, you can see tasks created with a plan within Teams, and they’re in sync.
This bug has been there for months but is made worse by the new restricted functionality of being unable to attach an existing plan to a team in Teams.
I have experienced that if I have a Plan that does not yet contain any tasks it will not be visible when I try to find it in "Existing plans". If I create a task in the plan it will be visible from teams when I browse existing plans. I do not know if this will solve your problem but hope it can be of help. Regards, Magnus