Autoscaling instance are protected from scale-in

The setting on the AutoScaling Group (ASG) is defining the default behavior for a newly launched instance. Disabling scale-in protection at the group level just means new instances don't launch with protection enabled by default. It can still be enabled on instances after they're launched via the ASG console or API. Check in CloudTrail fro the EventName SetInstanceProtection to see who is enabling it

Note: ASG scale-in protection is a different feature than EC2 Termination protection, so make sure you're looking at the right feature

Can you provide a little more information about this? Basically wondering if you're using launch configs, launch templates, the EC2 launch wizard, and where the termination protection was "disabled" (EC2 panel, in the template file, etc). The more we know about how those instances are set up/scaled out, will help find where the conflict between those settings may be.