
Laura,
People rarely look at older questions. Try asking again.
I installed the package in an old playground and verified it successfully.Then tried to uninstall and got this error message:
Component Type Name Problem
Flow Definition Post_Price_Changes_to_Slack The flow is still active. Deactivate the flow, and try again.
Flow Definition Opportunity_Status_Change The flow is still active. Deactivate the flow, and try again.
Flow Definition Price_Change_Push_Notification The flow is still active. Deactivate the flow, and try again.
Flow Definition Advertise_New_Property The flow is still active. Deactivate the flow, and try again.
Flow Definition Advertise_New_Property Component is in use by another component in your organization. Advertise_New_Property3010O000000UqXA
Flow Definition Post_Price_Changes_to_Slack Component is in use by another component in your organization. Post_Price_Changes_to_Slack3010O000000UqXC
Flow Definition Opportunity_Status_Change Component is in use by another component in your organization. Opportunity_Status_Change3010O000000UqXB
Flow Definition Price_Change_Push_Notification Component is in use by another component in your organization. Price_Change_Push_Notification3010O000000UqXD
I deactivated the 4 processes in Process Builder and was able to uninstall. Maybe this could work for you too - to uninstall the package in one playground and then install again.