Hi,

I'm getting an error where images sometimes disappear from the site after a deployment.

Umbraco 7.15.6 on Azure with flexible load balancing. Azure Blob Storage for media items.
Media cache is also stored in the blob.
Using Azure deployment slots.

It usually only affects the front end web app, the images appear correctly on the master (umbraco) web app and also on the staging slot.

Lots of these error messages appear in the logs:

Umbraco.Core.Sync.DatabaseServerMessenger - DISTRIBUTED CACHE IS NOT UPDATED. Failed to execute instructions (id: 15724, instruction count: 20). Instruction is being skipped/ignored
System.NullReferenceException: Object reference not set to an instance of an object.
   at Umbraco.Web.Cache.MediaCacheRefresher.ClearCache(JsonPayload[] payloads)
   at Umbraco.Web.Cache.MediaCacheRefresher.Refresh(String jsonPayload)
   at Umbraco.Core.Sync.DatabaseServerMessenger.NotifyRefreshers(IEnumerable`1 instructions, HashSet`1 processed)
   at Umbraco.Core.Sync.DatabaseServerMessenger.ProcessDatabaseInstructions(IReadOnlyCollection`1 instructionBatch, CacheInstructionDto dto, HashSet`1 processed, Int32& lastId)

Any ideas?

Many thanks.