Azure Function App: Deployment to staging slot deploys to production too

Question

We recently (within the last 4 weeks), discover a deployment issue when releasing new code. We use Azure Devops to deploy and have one 'staging' slot and one 'production' slot within Azure Functions. Both the function and devops environment have been running for almost a year without an issue. I'm also running two more functions app, in the same deployment / setting configuration without issue.

When I deploy to the staging slot, deployment is successful but the changes are live in both staging and production. How do I know? I'm adding a new function endpoint and can see this in both environments.

What I tried / confirmed...

Auto swap slot is not on

Recreated the publish task in Devops using the newer yaml format

Confirmed the deployment happens on both environments at the same time via the deployment logs

Confirmed in the production deployment logs that the last deployment was for the 'staging' slot - production deployments should only be via a swap

Published directly from Visual Studio, still had the same issue.

Any help / advise at this stage would be a great help.

Thanks