Let's say I have a matrix job with two configurations: ARM and x86.

I have files uploaded from each job, such that I have:

ARM/output_arm
x86/output_x86
x86/output_generic

I then have a second job, configured to download files from an Azure storage container of output from the first job - and I have a "Files to download (ant syntax)" set to "**/*_x86"

The Azure Storage plugin iterates each configuration of a matrix job separately, and considers an empty "Download from Azure Blob storage" set as an UNSTABLE-grade error - so this job would be marked UNSTABLE, because 0 files are downloaded in the ARM configuration.

17:51:31 MicrosoftAzureStorage - Downloading files from Azure Blob storage
17:51:31 MicrosoftAzureStorage - Failed to download files from Azure storage.
17:51:31  Verify that files exists with specified blob name   
17:51:31 Build step 'Download from Azure Blob storage' changed build result to UNSTABLE