So ran across this one today.
IF you are using StoreFront 2.0 AND auto-subscribe apps to your users (KEYWORDS:Auto in description) AND you see an event ID of 5 in the Citrix Delivery Services log on one of your StoreFront servers that is failing and the description is “The auto provisioned app with id “FarmName.AppName” has not bee subscribed during the last enumeration.”
Supposedly it manifests around 700+ subscriptions, although I have seen it hit as low as the 500 mark. (Calculate by <users> x <subscribed apps per user>)
This is particularly nasty because it defeats your load balancing even if you have a properly setup NetScaler utilizing StoreFront monitors..it will keep sending connections to the effected server rendering you with a random and nasty bug.
To check if this might be your issue go to a StoreFront server that is presenting the Event ID 5 with the above text and open PowerShell, Set-ExecutionPolicy Unrestricted, change to C:\Program Files\Citrix\Receiver StoreFront\Scripts and run .\ImportModules.ps1. Once complete, run a store subscription export by running Export-DSSStoreSubscriptions -StoreName <store> -FilePath c:\blah\subscriptions.csv and then open that CSV and see how many lines you have. If its in the hundreds then you might be effected by this bug.
Open a Citrix Support case and reference SR 61125582 for the private hot fix. Word is this will be included in StoreFront 2.1.
Happy <bug> hunting