[1.2.1] Error Code 5 — lobby works, every Skirmish (PvE) match fails (China)

[xiaobai]

Summary
Since updating to 1.2.1 (Unity 6), I can enter the lobby normally, but starting any Skirmish match (PvE, against AI) fails with "Connection error. Code: (5)". It fails 100% of the time. I have not tested PvP.

Environment

• Game version: 1.2.1 (Unity 6.3.24f1)
• OS: Windows 11
• Store: Steam
• Location: China
• Region tried: Global and CIS — both fail

Symptom

• Lobby connects fine. Client log shows normal traffic: InBytes ~1800, OutBytes ~900, LiveTime 7-20 sec.
• I create a Skirmish (PvE) game and press start. The client connects to the game server and exchanges packets for about 14 seconds.
• After that the server stops responding. The client keeps sending 29-byte heartbeats every 5 seconds, gets no reply, and gives up.
• Client log after 8 attempts: InBytes: 0, OutBytes: 0, LiveTime: 0 sec, Timeout: True
• This is a PvE match with no other human players involved, so it does not depend on peer-to-peer or NAT.

Evidence
I captured traffic with pktmon on the game port. The connection IS established and data flows both ways before it dies:

Code: Select all

21:00:31  handshake complete, bidirectional packets (1044 / 1146 / 1302 bytes)
21:00:31-45  continuous two-way traffic
21:00:45  last response from server
21:00:55 / 01:00 / 01:05 / 01:10  client sends 29-byte heartbeat, no reply

Inbound UDP packets DO reach the NIC (verified at the TcpIp layer). Yet the client reports InBytes: 0. So the packets arrive but never reach the game logic.

Already ruled out (all tested)

• Windows Firewall completely disabled — no change
• Antivirus (Huorong) network protection disabled — no change
• VPN / global proxy — no change
• Game accelerator in route/TUN mode — no change
• IPv6 / Teredo disabled — no change
• DNS and hosts file — clean
• Phone hotspot on a different ISP — no change
• Server region: Global and CIS — both fail
• Steam "verify integrity of game files" — passed, no errors
• Deleted local cache and reconnect data — no change

Question
Is this a known regression from the Unity 6 networking rewrite in 1.2.1? The same machine and network worked fine before 1.2.1.

I can provide the full client log and the pktmon capture if that helps.