Subject Open database connection fails

I have a strange behavior. In my windows-service application i try to open a database connection, but i some cases it fails.

The file are installed on Windows 10 on a notebook. When the computer boots with a network connection and Internet are on. My program works without any problems. But when the computer are booting an the network are not connected, the windows-service starts and trys to connect to the database, but it wil fails with a exception.

For test purposion, i istalled the EMS-Manager to connect also to the database file, this will works without any problems!

So EMS-Manager can connect, my service-apps can not connect when the notebook are started without a network pluged in.

I developed my service-app with Delphi 10.3.1 and FireDAC. The database are Firebird 3.0.4

the catched exception are
  2.1 Date          : Fri, 14 Jun 2019 11:36:14 +0200
  2.2 Address       : 008D0CA6
  2.3 Module Name   : AquaStar_Service.exe - (AquaStar_Service)
  2.4 Module Version:
  2.5 Type          : EIBNativeException
  2.6 Message       : [FireDAC][Phys][FB]Unable to complete network request to host "localhost".
                      Failed to locate host machine.
                      The specified name was not found in the hosts file or Domain Name Services.

Operating System:
  6.1 Type                : Microsoft Windows 10 (64 bit)
  6.2 Build #             : 1803 (10.0.17134.829)
  6.3 Update              : April 2018 Update [Redstone 4] #829
  6.4 Non-Unicode Language: French (080C)
  6.5 Charset/ACP         : 0/1252
  6.6 Install Language    : French (040C)
  6.7 UI Language         : French (040C)
  6.8 Edition             : Enterprise

I also tryed to restart my service-app, but it dosen't helped!

May somebody has me a hint.

Best Regards