Exchange Server: Active Sync client has connect/sync issues

[German]Microsoft addresses synchronization issues with Active Sync in connection with Exchange server environments in a recent KB article. Here is some information that might be helpful for Exchange administrators.

Yesterday night @PhantomofMobile on Twitter made me aware of an Exchange server issue and a kb article from Microsoft.

ACTIVE SYNC CLIENT CONNECTION OR SYNCHRONIZATION ISSUES:

Thank You: @SBSDiva

ICYMI: @woodyleonhard @AdminKirsty @thurrott @maryjofoley @bdsams @mehedih_ @ruthm @etguenni @SwiftOnSecurity @pcper @MalwareJake @GossiTheDog @ryanshrout @JobCackahttps://t.co/peVDiUuYym

— Crysta T. Lacey (@PhantomofMobile) 16. Oktober 2018

Microsoft describes a scenario that can occur in environments with Exchange Server 2016 or Exchange Server 2013 in conjunction with an Active Sync client in a KB article titled ActiveSync clients cannot connect or synchronizing is delayed in an Exchange Server environment (4456227).

The error description for Active Sync

In a Microsoft Exchange Server 2016 or Exchange Server 2013 environment, ActiveSync clients will not be able to connect or there will be delays when users synchronize their mobile devices.

In addition, all features of the CAS role will no longer work. This problem occurs after the ActiveSync application pool has been running for some time, typically several weeks. In addition, the following behavior may occur: 

• Event ID 4227 is logged within the system log of the Event Viewer.
• The ActiveSync application pool consumes a lot of disk space.
• The .NET CLR value Memory/% Time in the GC counter for the w3wp instance corresponding to the ActiveSync application pool is unusually high.
• There is an exhaust of the TCP port due to the large number of requests in ActiveSync. 
• The counter W3SVC_W3WP/Active Requests for the instance MSExchangeSyncAppPool shows a steadily increasing value over several days or weeks. 
• The netstat -anob command can display many connections in a CLOSE_WAIT state.

Microsoft classifies this as a known problem that occurs when ActiveSync ping commands get stuck in the application pool.

Workaround for Exchange Server 2013

For Exchange Server 2013, Microsoft describes only a workaround. You should regularly empty the ActiveSync application pool for all servers to release individual (pending) commands. 

For more information about configuring an application pool to automatically recycle at regular intervals, see the document "Recycling Settings for an Application Pool <recycling>" on the Microsoft Docs Web site. This description has existed since 2016..

A fix for Exchange Server 2016

Effective October 17, 2018, Microsoft added a fix for Exchange Server 2016 to older KB articles with the Workaround for Exchange Server 2013. In Exchange Server 2016 environments, install Cumulative Update 11 for Exchange Server 2016 or a higher Cumulative Update for Exchange Server 2016. Then the error should no longer occur.