Hi, I saw there is already a thread on this, but apparently I can't respond on that thread for whatever reason.
So here's the issue: To most people I can connect properly but now and then someone joins with whom i happen to be fp and if that happens the whole room gets fp suddenly and if I close the room voobly will crash.
It's quite annoying and I talked to other people who know the issue (plus there's already a thread on this issue) so I think it's a bug in voobly and has nothing to do with my internet configuration. Especially since voobly will crash under the mentioned circumstances.

Here's the link to the other thread
https://www.voobly.com/forum/thread/351757

Please paste us the results of the network diagnostics here. You can find the network diagnostics tool in the lobby menu, please run it, wait for the results and then share the result with us here. Thank you.

If you experience crashes as well, please also run the game diagnostics tool and share the result with us here.

Starting networking diagnostics...

Your local network port (UDP) is 16000. All game traffic is routed through this port. This can be changed in "Settings" -> "NAT Traversal".

Attempting to connect to 3 test servers. This will take around a minute to complete...

Received data from 'server 1' through port 16000 (this is your WAN or router port)
Received data from 'server 3' through port 16000 (this is your WAN or router port)
Received data from 'server 2' through port 16000 (this is your WAN or router port)
14 seconds left.
9 seconds left.
4 seconds left.

Test Result: All Pass
Network Health: All tests passed
Recommended Action: None
Details: All tests passed.

For help understanding this report or for more information go to http://www.voobly.com/pages/view/177#Network_Diagnostic_Tool.

Non-DirectPlay game path is 'C:\Program Files (x86)\Microsoft Games\Age of Empires II'
Verifying 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\language_x1.dll' exists...
Success!
Verifying 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\age2_x1\age2_x1.exe' exists...
Success!
Voobly path is 'c:\program files (x86)\voobly'
Game version is '1.0C-VLY'
Verifying 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\language_x1_p1.dll' exists...
Success!
Checking DirectPlay libraries...
Looking for dpwsockx.dll...
Looking for dplayx.dll...
'c:\windows\system32\dplayx.dll' size: 215552 bytes
DirectPlay Init Success!
Scanning installed DirectPlay games...
Age of Empires II
Age of Empires II - The Conquerors Expansion [found]
Game was found in DirectPlay registry!
DirectPlay play thinks the game is installed at 'C:\Program Files (x86)\Microsoft Games\Age of Empires II'
DirectPlay command line is 'lobby'
DirectPlay play thinks the game exe is at 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\Age2_X1\age2_x1.exe'
Verifying file exists... Success!
DirectPlay play thinks the language dll is at 'C:\Program Files (x86)\Microsoft Games\Age of Empires II\language_x1.dll'
Verifying file exists... Success!
Scanning 'c:\program files (x86)\voobly\gamedata\AOC\age2_x1.exe'
Success!

Everything looks fine. DirectPlay is configured and the game was found on your harddrive. If you still have problems try rejoining the lobby or restarting your computer.

Network Diagnostics looks fine. You should try performing a clean installation of the Voobly client:
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I will try that but actually I'm not confident if it helps. I read in another thread (which I can't find anymore ) that theres some kind of voobly log file that gets overwritten with each restart of the client. Do you know what I mean and can you tell me where to find it? If it might help, I can post the log file next time my voobly client crashes due to this weird fp error.

When the client is crashing, upload the Voobly.txt here BEFORE restarting the client.
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Okay so the reinstall didnt help. Had the same issue some minutes ago. Restarted voobly too quickly and forgot about the voobly.txt though. I will post it next time it happens. It might take a while, since it doesnt happen too regularly so please leave this thread open.

That was quicker than expected. So here I had the issue again.
I paste the part from where the concerning user (PapinSantola) joined the room:

18:43:08 NAT1: [18:43:08] [User: PapinSantola] Local User: Pooping_Pony, Remote User: PapinSantola
18:43:08 NAT1: [18:43:08] [User: PapinSantola] [Tunnel: direct] State changed to DCC_INIT
18:43:08 NAT1: [18:43:08] [User: PapinSantola] Sending local candidate port list, LAN Port = 16000, WAN Port = 16000, User Proxy = :0
18:43:09 NAT1: [18:43:09] [User: PapinSantola] Peer ack'ed local candidate port list
18:43:09 NAT1: [18:43:09] [User: PapinSantola] Received remote candidate port list, LAN Port = 16000, WAN Port = 16000, User Proxy = :0
18:43:09 NAT1: [18:43:09] [User: PapinSantola] [Tunnel: user proxy] No user proxy specified
18:43:09 NAT1: [18:43:09] [User: PapinSantola] [Tunnel: direct] State changed to DCC_TUNNEL_TEST
18:43:09 NAT1: [18:43:09] [User: PapinSantola] [Tunnel: fast proxy] Received PH_TYPE_TUNNEL_TEST_ACK
18:43:09 NAT1: [18:43:09] [User: PapinSantola] [Tunnel: fast proxy] Proxy -> FPS_ALIVE
18:43:09 NAT1: [18:43:09] [User: PapinSantola] [Tunnel: direct] in port change from 0 to 16000
18:43:09 NAT1: [18:43:09] [User: PapinSantola] [Tunnel: direct] Received PH_TYPE_DIRECT_TEST - port = 16000
18:43:09 NAT1: [18:43:09] [User: PapinSantola] [Tunnel: fast proxy] Received PH_TYPE_TUNNEL_TEST
18:43:10 NAT1: [18:43:10] [User: PapinSantola] [Tunnel: direct] Received PH_TYPE_DIRECT_TEST_ACK_ACK
18:43:24 NAT1: [18:43:24] [User: PapinSantola] [Tunnel: direct] Trouble connecting to PapinSantola -- increasing scan range
18:43:26 Alert and window is active
18:43:26 sound = theme/voobly2/sounds/message.wav. bFlash = 0, bAlert = 0, bSound = 0
18:43:28 Alert and window is active
18:43:28 sound = theme/voobly2/sounds/message.wav. bFlash = 0, bAlert = 0, bSound = 0
18:43:36 NAT1: [18:43:36] [User: sky_Gjun] Error: peer isn't responding
18:43:36 NAT1: [18:43:36] [User: van3263] Error: peer isn't responding
18:43:36 NAT1: [18:43:36] [User: dinar87] Error: peer isn't responding
18:43:39 NAT1: [18:43:39] [User: PapinSantola] [Tunnel: direct] State changed to DCC_TUNNEL_CONNECTION_FAILED
18:43:39 NAT1: [18:43:39] [User: GalindoPotas] Error: peer isn't responding
18:43:39 NAT1: [18:43:39] [User: minafayek] Error: peer isn't responding
18:43:39 NAT1: [18:43:39] [User: thalismav87] Error: peer isn't responding
18:43:41 CGameRoom::~CGameRoom
18:43:41 NAT3: CNatGame::CleanState IN, m_UserIDs.Count() = 7
18:43:41 NAT3: CNatGame::ThreadEntry OUT
18:43:42 NAT3: CNatCommunication::ThreadEntry OUT
18:43:42 NAT3: CNatGame::CleanState OUT
18:43:42 NAT1: CNatHelper::ThreadEntry OUT

Before he entered I was connected to everyone except him. He was first connecting, then went fp, then all the other players went fp and when I closed the room voobly crashed.
Tell me if you need the full copy, I can provide, but I guess you only need the part with the concerning user?

I need the full log file please since the log snippet just shows the failed NAT-T handshake.

Click Reply instead of using Quick Reply below and attach the log file please.

Here you go

Question: does Voobly simply close for you or does it crash, e. g. "Not Responding" message?

The whole program will just close. No error message.

Can you please upload further logs, every time this happens? Thanks.