I am getting the same issue on Windows Server 2008 R2 64-bit.

When running x64 I get the same error in RPT as OP: Initializing Steam server failed

And when a client joins the RPT shows: Client: [VB]AWOL - Kicked off because of invalid ticket: Invalid ticket - Ticket invalid

x86 works: Initializing Steam server - Game Port: 2302, Steam Query Port: 2303

Dependancy Walker reports missing dll's for the arma3sever_x64.exe
API-MS-WIN-CORE-WINRT-ERROR-L1-1-0.DLL
API-MS-WIN-CORE-WINRT-L1-1-0.DLL
API-MS-WIN-CORE-WINRT-ROBUFFER-L1-1-0.DLL
API-MS-WIN-CORE-WINRT-STRING-L1-1-0.DLL
DCOMP.DLL
IESHIMS.DLL
MFPLAT.DLL
OPENAL32.DLL
PHYSX3_X64.DLL
PHYSX3COMMON_X64.DLL
PHYSX3COOKING_X64.DLL
WLANAPI.DLL

as does steam_api64.dll
API-MS-WIN-CORE-WINRT-ERROR-L1-1-0.DLL
API-MS-WIN-CORE-WINRT-L1-1-0.DLL
API-MS-WIN-CORE-WINRT-ROBUFFER-L1-1-0.DLL
API-MS-WIN-CORE-WINRT-STRING-L1-1-0.DLL
DCOMP.DLL
IESHIMS.DLL
MFPLAT.DLL
WLANAPI.DLL

Also, I have every Visual Studio C++ Redistributable (x86 and x64 - 2005, 2008, 2010, 2012, 2013 and 2015) installed.

I was also having the same issue earlier on today with dev branch, both on server 2012 R2 and locally with Windows 10, all redists from 2005-2015, unfortunately don't have much more in regards to debugging info but the issue isn't isolated to one person.

workaround is install steamclient and just let it running on login screen
fix is wip , no eta for now

Yep.

I can confirm that starting steam to the login window(on server) solved the problem!
I just tested it out. The server shows up in launcher as well!

1. Start steam to login-window
2. Start the arma3_64bit-server.exe

Let´s see how good the performance will be :)

In T123437#1576952, @Dwarden wrote:

workaround is install steamclient and just let it running on login screen
fix is wip , no eta for now

Edit: Just read G-susOnSteroids' comment, thats my question answered! :)

Does this mean just have the client running but not logged in or do you have to log in? If the latter is the case I then assume there is no use testing on dedicated unless you have an alternate steam account with the game? Since steam signs out other locations.

Kind regards,
KamikazeXeX

Yep,

you don´t need to log in. Just start steam and thats all. (on server)

Greets

Installed and ran steamclient, opened to login screen only and x64 A3 server gives me the same results.

Initializing Steam server failed

In T123437#1577699, @vbawol wrote:

Installed and ran steamclient, opened to login screen only and x64 A3 server gives me the same results.

Initializing Steam server failed

By any chance do you use FireDaemon or something similar to run the server etc? I personally use FireDaemon and I had to revert to starting via batch files to get it to work, Steam being running had no effect on it when it was running in session 0.

Yes I do use FireDaeamon.

Update: I did get it running using a shortcut.

Can anyone confirm if Battleye Rcon is working, with this method of starting x64 server?
EDIT: rcon issue was I was just missing beserver_x64.cfg

In T123437#1578231, @vbawol wrote:

Can anyone confirm if Battleye Rcon is working, with this method of starting x64 server?

Battelye has never worked on dev/RC for me, always results in unknown game version when joining the server so I've always had it turned off when in dev/RC branch