Hi Marc,
The green check-mark is not turned on and snapshots are not being created. I have no idea why this is happening. I looked at every log file to try to find a reason, but I I could not find an error related to this. As explained, the IAM user I am using in Scalr have appropriate permissions, I can trigger a manual snapshot and it works, I can view snapshots, I can view volumes. I have 4 other environments configured exactly the same and everything is working fine. The only difference I could find is that this is the only volume hosted in region us-east1b, others in other environments are in different sub-region, like us-east1a or 1c.
I have also tried to create a volume from Scalr and enable auto-snapshot on it, but same behaviour and auto-snapshot stays disabled.
Here's some screen capture: