Amazon Connect forecast says insufficient data but I loaded a year

How many months? Documentations states 6 months.

You have less than 6 month of historical data. To address this problem, upload more historical data. While Amazon Connect can generate forecasts with six months of data, we recommend at least 12 months of recent contact data to ensure that contact patterns (for example, seasonality) are properly captured. If you don’t have 6 months of data, you can give Connect synthetic (artificial) data that will be used to generate the forecast. Alternately, you can upload your own forecast using the Override function.

You need at least 2,000 contacts per month across all of your forecast groups. Amazon Connect generates forecasts using historical data for all queues that are included across all forecast groups. At least 2,000 monthly contacts in the past 6 months for the Amazon Connect instance are required to successfully generate a forecast. Amazon Connect does not require 2,000 monthly contacts for every queue. All queues in all forecast groups must total more than 2,000 monthly contacts.

You need recent data. Amazon Connect performs a data recency check (is the data recent enough) based on the aggregation of all queues included across all forecast groups. At least one data point in the past four weeks is required to successfully generate a forecast.

https://docs.aws.amazon.com/connect/latest/adminguide/troubleshooting-forecasting-capacity-planning-scheduling.html