Elastic Beanstalk platform update doesn't update AMI

We're running 4 environments of the same application on Elastic Beanstalk, using the Docker running on 64bit Amazon Linux 2 platform.

Doing platform updates (either automatically during the maintenance window or triggered manually using the "Platform, Change version" button on the console) replace the instances adhering to the deployment settings (batch size, minimum instances) as expected. After platform update finishes, 2 of our environments are in the expected state (instances running with the latest AMI), however the other 2 environments are still running the old AMI. Beanstalk reports that all of the enviroments are running the latest platform, but this is obviously incorrect. We are able to manually fix the affected 2 environments by manually overriding the AMI ID for the environments, however we'd like to have this done automatically.

Comparing the configuration between the environments doesn't show any obvious differences that could cause this behaviour.

Any help or advice would be appreciated.