VM start, reapply and redeploy fail with a disk related error

Question

Hello everyone!
I hope someone can help with this weird issue I ran into.
I have a VM that suddenly began failing to start with this error:

Failed to operationname the virtual machine vmname. Error: The disk/snapshot resource with id resourcegroupname/providers/Microsoft.Compute/disks/osdiskname'>osdiskname cannot be resized down. Reducing disk/snapshot size is not supported in Azure to prevent data loss. If you do need to reduce the size of the disk, please create new snapshot/disks with the appropriate size. More information is available at https://aka.ms/AzureDisksFAQ. Target: '/subscriptions/subscriptionid/resourceGroups/resourcegroupname/providers/Microsoft.Compute/disks/osdiskname'.

This is really unexpected, because there have been no changes to any part of that VM since the last time it worked normally. I tried redeploying and reapplying, but those operations fail with the same error.
Anyone seen something like this or have any ideas?

Answer 1

Latest update: problem solved.
What I did was: I took a snapshot of the disk. I created a "dummy" disk out of the snapshot and attached it to the VM. I deleted the original disk and I created a new disk from the snapshot, using the original disk name. I attached this latest disk to the VM and I was able to start it.

Complete mystery!