When I hit start and type "Active", for example, the start menu correctly finds "Active Directory Users and Computers", "Active Directory Domains and Trusts", etc. on Windows 10 and Windows 2012R2.
that is NOT the case in Windows 2016 TP5. I have to type in "administrative" to get to "Windows Administrative Tools" and then run my mmc.

I don't know if it is a setting I should enable (maybe Cortana), or I have to wait for some indexing to finish (I've already waited waaay to long; besides Windows 2012R2 does not have this index-wait-time) for this comprehensive search to happen, but now the search function on start menu of Windows 2016 TP5 does not return all the relevant results as it does in other previous versions.

I am working on a new lockdown group policy that will be used for our future Windows 2016 XenApp servers.

As this will be used for a lot of users, certain things will need to be locked down. For example the Settings need to be locked down in the same way as it possible with Control Panel.

I want to be able to manage what settings is visible in Settings with GPO.

We cannot allow users on a shared RDSH server to install windows update, add VPN connection, check what application is installed etc etc.
With Control Panel it was possible to hide certain settings, with Settings its all or nothing.

Scheduled tasks on the current TP5 of Windows Server 2016, which have a CalendarTrigger with repetition configured, don't seem to trigger and cannot be started manually.
The same trigger without repetition (e.g. after unchecking the "Repeat task every:" checkbox in taskschd.msc) works correctly.
A TimeTrigger with the same repetition configuration works, too.
taskschd.msc calculates and displays the next runtime correctly.

When I try to start such a task manually in taskschd.msc, a message box appears (running any other task works):
de-DE: "Der Aufgabenplanungsdienst ist nicht verfügbar. Die Aufgabenplanung wird erneut versuchen, eine Verbindung herzustellen."
en-US: "Task Scheduler service is not available. Task Scheduler will attempt to reconnect to it."

When I try to start the task by using Start-ScheduledTask, a non-terminating exception is thrown ("Nicht implementiert"="Not Implemented"):
PS C:\Users\Administrator> Start-ScheduledTask -TaskName bad
Start-ScheduledTask : Nicht implementiert
In Zeile:1 Zeichen:1
+ Start-ScheduledTask -TaskName bad
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (PS_ScheduledTask:Root/Microsoft/...S_ScheduledTask) [Start-ScheduledTask]
, CimException
+ FullyQualifiedErrorId : HRESULT 0x80004001,Start-ScheduledTask

When I try to start it via schtasks.exe, the same message appears:
C:\Users\Administrator>schtasks /run /tn bad
FEHLER: Nicht implementiert

When the task should trigger by time, there are no events in Microsoft-Windows-TaskScheduler/Operational indicating any activity around this task.

The tasks trigger sections look like this:
working (without repetition):
<Triggers>
<CalendarTrigger>
<StartBoundary>2016-06-14T00:13:00</StartBoundary>
<Enabled>true</Enabled>
<ScheduleByDay>
<DaysInterval>1</DaysInterval>
</ScheduleByDay>
</CalendarTrigger>
</Triggers>
not working (with hourly repetion):
<Triggers>
<CalendarTrigger>
<Repetition>
<Interval>PT1H</Interval>
<Duration>P1D</Duration>
<StopAtDurationEnd>false</StopAtDurationEnd>
</Repetition>
<StartBoundary>2016-06-14T00:13:00</StartBoundary>
<Enabled>true</Enabled>
<ScheduleByDay>
<DaysInterval>1</DaysInterval>
</ScheduleByDay>
</CalendarTrigger>
</Triggers>

On Windows Server 2012R2 this task works perfectly fine.

Test environment (in case it matters):
Hyper-V Generation 2 VMs on Windows Server 2012R2
Windows Server 2016 Technical Preview 5 Standard with GUI German (installed from de_windows_server_2016_technical_preview_5_x64_dvd_8512319.iso, SHA1 20B276A6EF63AB46FF50A561CD16B48FDF8787AE)
3 VMs, 2 of them fresh installs without any modification except the task

The whole task:
<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.4" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
<RegistrationInfo>
<Date>2016-06-14T10:20:18.9077118</Date>
<Author>WIN-B5GC2VET9K1\Administrator</Author>
<URI>\Test</URI>
</RegistrationInfo>
<Triggers>
<CalendarTrigger>
<Repetition>
<Interval>PT1H</Interval>
<Duration>P1D</Duration>
<StopAtDurationEnd>false</StopAtDurationEnd>
</Repetition>
<StartBoundary>2016-06-14T00:13:00</StartBoundary>
<Enabled>true</Enabled>
<ScheduleByDay>
<DaysInterval>1</DaysInterval>
</ScheduleByDay>
</CalendarTrigger>
</Triggers>
<Principals>
<Principal id="Author">
<UserId>S-1-5-18</UserId>
<RunLevel>LeastPrivilege</RunLevel>
</Principal>
</Principals>
<Settings>
<MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
<DisallowStartIfOnBatteries>true</DisallowStartIfOnBatteries>
<StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
<AllowHardTerminate>true</AllowHardTerminate>
<StartWhenAvailable>false</StartWhenAvailable>
<RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>
<IdleSettings>
<StopOnIdleEnd>true</StopOnIdleEnd>
<RestartOnIdle>false</RestartOnIdle>
</IdleSettings>
<AllowStartOnDemand>true</AllowStartOnDemand>
<Enabled>true</Enabled>
<Hidden>true</Hidden>
<RunOnlyIfIdle>false</RunOnlyIfIdle>
<DisallowStartOnRemoteAppSession>false</DisallowStartOnRemoteAppSession>
<UseUnifiedSchedulingEngine>false</UseUnifiedSchedulingEngine>
<WakeToRun>false</WakeToRun>
<ExecutionTimeLimit>PT72H</ExecutionTimeLimit>
<Priority>7</Priority>
</Settings>
<Actions Context="Author">
<Exec>
<Command>C:\temp\test.bat</Command>
</Exec>
</Actions>
</Task>