We're running a site (Umbraco v7.5.14) on Azure Web Apps. All the recommended settings for Azure have been set.

Occasionally there is a flurry of error messages in the log that mention an issue with a crypographic hash:

2018-02-08 13:25:26,093 [P7232/D3/T265] ERROR Umbraco.Core.UmbracoApplicationBase - An unhandled exception occurred
System.Security.Cryptography.CryptographicException: Hash not valid for use in specified state.
at Umbraco.Core.Cache.HttpRuntimeCacheProvider.GetCacheItem(String cacheKey, Func`1 getCacheItem, Nullable`1 timeout, Boolean isSliding, CacheItemPriority priority, CacheItemRemovedCallback removedCallback, CacheDependency dependency)
at Umbraco.Core.Cache.HttpRuntimeCacheProvider.GetCacheItem(String cacheKey, Func`1 getCacheItem, Nullable`1 timeout, Boolean isSliding, CacheItemPriority priority, CacheItemRemovedCallback removedCallback, String[] dependentFiles)
at Umbraco.Core.Cache.DeepCloneRuntimeCacheProvider.GetCacheItem(String cacheKey, Func`1 getCacheItem, Nullable`1 timeout, Boolean isSliding, CacheItemPriority priority, CacheItemRemovedCallback removedCallback, String[] dependentFiles)
at Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedMediaCache.GetCacheValues(Int32 id, Func`2 func)
at Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedMediaCache.GetUmbracoMedia(Int32 id)
at Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedMediaCache.GetById(UmbracoContext umbracoContext, Boolean preview, Int32 nodeId)
at Umbraco.Web.PublishedCache.ContextualPublishedCache`1.GetById(Boolean preview, Int32 contentId)
at Our.Umbraco.PropertyConverters.MultipleMediaPickerPropertyConverter.ConvertSourceToObject(PublishedPropertyType propertyType, Object source, Boolean preview)
at Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.get_Value()
at Umbraco.Web.PublishedPropertyExtension.GetValue[T](IPublishedProperty property, Boolean withDefaultValue, T defaultValue)
at Umbraco.Extensions.Models.ModelLogic.CreateMasterModel(IPublishedContent content)
at Umbraco.Extensions.Models.ModelLogic.CreateMasterModel()
at ASP._Page_Views_Master_cshtml.Execute() in d:\home\site\wwwroot\Views\Master.cshtml:line 5

Has anyone seen this issue before?

Could it be a configuration issue, or maybe something else?