On PC (Steam), MTG Arena repeatedly shows “Network Error” or “Unable to get collection” when IPv6 is enabled.
The issue occurs on a valid dual-stack network: both IPv4 and IPv6 routes are reachable, but the client never retries on IPv4 if IPv6 stalls.

Steps to reproduce

Launch MTG Arena on a Windows system with IPv6 preferred (e.g. Fritz!Box router).

Start the client — it hangs with Network Error.

Launch again using:

C:\Windows\System32\cmd.exe /c "set PREFERIPV4=true && set UNITYIPV6=0 && start "" "C:\SteamLibrary\steamapps\common\MTGA\MTGA.exe""

The game connects normally.

Actual result:
Arena fails to connect when IPv6 path is slow or unreachable.

Expected result:
Client should automatically fall back to IPv4 per RFC 6555 (“Happy Eyeballs”).

Workaround:
Setting PREFERIPV4=true and UNITYIPV6=0 forces IPv4-only sockets and resolves the problem immediately.