Cannot connect using to Server 2019 using rdp app on Windows 10, iOS or Windows Mobile

I can connect to my server using the desktop app on Windows 10. (I am not using a gateway.)

If I however use the UWP Windows 10 app (from the Store), or the iOS app from the AppStore, or the RDP app from Windows Mobile from the Store I cannot connect from within the LAN nor from the internet and get the following series of events on the server:

Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS103RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS145RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS102RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS72RemoteFX module
Warning26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS144RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS141RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS72RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS72RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS65RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS131RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS103RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS145RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS102RemoteFX module
Information26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS72RemoteFX module
Warning26-6-2019 13:04:01RemoteDesktopServices-RdpCoreTS144RemoteFX module
Information26-6-2019 13:03:43RemoteDesktopServices-RdpCoreTS141RemoteFX module
Information26-6-2019 13:03:43RemoteDesktopServices-RdpCoreTS72RemoteFX module
Information26-6-2019 13:03:43RemoteDesktopServices-RdpCoreTS72RemoteFX module
Information26-6-2019 13:03:43RemoteDesktopServices-RdpCoreTS65RemoteFX module
Information26-6-2019 13:03:43RemoteDesktopServices-RdpCoreTS131RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS103RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS148RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS145RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS102RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS72RemoteFX module
Warning26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS144RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS141RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS72RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS72RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS65RemoteFX module
Information26-6-2019 13:03:38RemoteDesktopServices-RdpCoreTS131RemoteFX module

The last event 103 in detail:

Log Name:      Microsoft-Windows-RemoteDesktopServices-RdpCoreTS/Operational
Source:        Microsoft-Windows-RemoteDesktopServices-RdpCoreTS
Date:          26-6-2019 13:04:01
Event ID:      103
Task Category: RemoteFX module
Level:         Information
Keywords:      
User:          NETWORK SERVICE
Computer:      [Domain]
Description:
The disconnect reason is 14
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-RemoteDesktopServices-RdpCoreTS" Guid="{1139c61b-b549-4251-8ed3-27250a1edec8}" />
    <EventID>103</EventID>
    <Version>0</Version>
    <Level>4</Level>
    <Task>4</Task>
    <Opcode>17</Opcode>
    <Keywords>0x4000000000000000</Keywords>
    <TimeCreated SystemTime="2019-06-26T11:04:01.400433100Z" />
    <EventRecordID>25927928</EventRecordID>
    <Correlation ActivityID="{f4208e27-0719-4d0a-aa89-7ba13ae70000}" />
    <Execution ProcessID="396" ThreadID="8172" />
    <Channel>Microsoft-Windows-RemoteDesktopServices-RdpCoreTS/Operational</Channel>
    <Computer>[Domain]</Computer>
    <Security UserID="S-1-5-20" />
  </System>
  <EventData>
    <Data Name="ReasonCode">14</Data>
  </EventData>
</Event>

The mobile apps work just fine connecting to my Windows 10 PC.

If there is anybody who can shed light on this, I would be very grateful.

---

Leo

Edit: I would like to add that the error message on the client is: 

Your password may have expired or the remote pc might not accept blank passwords