Azure Devops environment variable gets cross contaminated when run in parallel

We have a pipeline with a number of environments to deploy onto; dev, qa, iat, preprod. We do a build, some checks & deploy to dev. Once that part has completed the next three environments are gated & we can run them all in parallel or one at a time.

We currently have to run this pipeline one at a a time for qa, iat & vNextIat because the environment variable appears to be contaminated from one of the other environments.

The error refers to an attempt to retrieve the state from the wrong storage account:

The image shows the IAT deployment failing as it tries to get the state file (I think) from the vNextIat environment. The pksvnextiatsa is the storage account from within the vnextiat environment. It should be targeting pksiatsa (its a simple naming scheme).

• Why is this happening?
• Why is it ok when ran on its own?
• How can I fix this?

To be clear, because of the gates they aren’t kicked off at exactly the same time but quickly one after the other. Always fails when more than one of them is running & always seems to be attempting to get the next environments resources. Not always but mostly.