There was likely a conflict between the low usage alarm of the target tracking policy and the scheduled scaling action. To prevent this, increase the MinSize of the ASG instead of the desired. That way the scaling policy can't scale-in while the usage is still low before your traffic spike hits. You'll then want a 4th scheduled action a little while later (any time after your traffic spike will have started) that lowers the Min back down to 3. This way the target tracking policy can still gracefully scale-in the ASG when the utilization goes down. You could optionally also still keep the scheduled action that sets Desired to 10.
As a side note: It sounds like you're using ECS. I'd recommend looking into CapacityProviders, which have a special metric designed for scaling ASGs that are used for ECS clusters which you can replace your current target tracking policy with: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/asg-capacity-providers.html#asg-capacity-providers-managed-scaling
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