The borderlands 4 coop disconnects pattern in patch 1.4 has three flavors: connection refused before you join, random drops 15 to 30 minutes into a session, and a hard crash when the host migrates after a wipe. We have logged all three with tracert and Steam Networking debug overlay across four ISPs. The fixes below cover the network side (NAT, UPnP, ports), the platform side (Steam Friends sync, party state), and the patch-specific bugs Gearbox has acknowledged.

Why this happens

Borderlands 4 multiplayer uses Steam Networking Sockets (SNS) — a relay-and-NAT-punching protocol that Valve operates on top of UDP. SNS needs at least one of three things to succeed: UPnP-opened ports on your router, manually forwarded Steam ports, or a relay server that both peers can reach. If none work, you sit at “Connecting” forever or get borderlands 4 coop disconnects within minutes.

Patch 1.4 also introduced two known issues. First, Steam Friends presence is cached for too long and shows friends as offline who actually joined a different lobby. Second, host migration after a death-screen wipe can crash the migrating host because the engine tries to re-spawn loot before the new host’s world state is fully committed. Both are documented in the 1.5 PTR notes.

5 fixes ranked by likely effectiveness

1. Open your NAT via UPnP

Most home routers support UPnP and Steam will request the right ports automatically. Just confirm UPnP is on.

Router admin page (commonly 192.168.1.1 or 192.168.0.1)
  -> Advanced or Forwarding
  -> Enable UPnP: On
Reboot the router. In Steam: View -> Settings -> Downloads -> Clear download cache.

Then in Steam:

View -> Settings -> In-Game
  -> Show Network Status (right-click status bar) should show "Relay" or "P2P (Direct)"

Skip if UPnP is disabled by your ISP-supplied router and you cannot turn it on — go to fix 2.

2. Manually forward Steam Networking ports

If UPnP is locked down, forward these ports to your gaming PC’s local IP.

UDP 27015-27050   (Steam game traffic)
UDP 3478, 4379, 4380   (Steam Voice and SNS)
TCP 27015-27030   (Steam client)

Find your local IP:

Get-NetIPAddress -AddressFamily IPv4 | Where-Object {$_.InterfaceAlias -notmatch "Loopback"}

Linux / Steam Deck:

ip -4 addr show | grep inet

Forward each port range to that local IP in your router admin page. Skip if you are on double NAT (modem + router both NAT) — call your ISP and request bridge mode.

3. Refresh Steam Friends and party state

Patch 1.4 caches friend presence aggressively. Force a refresh.

1. Quit Borderlands 4 completely.
2. In Steam: right-click a friend who you cannot see in BL4 -> Invite to Game (any other game).
3. Cancel the invite.
4. Visit: steam://friends/refresh in your browser.
5. Relaunch BL4 and re-invite from the in-game friends panel.

This forces Steam to re-fetch presence handles. Skip if you can already see your friend’s BL4 status correctly — the bug is not on your end.

4. Disable Steam Family Beta until patch 1.5

The Steam Families beta breaks BL4 friend presence in a way Gearbox has acknowledged.

Steam -> Settings -> Family
  -> Leave Steam Families Beta
Quit and relaunch Steam.

Skip if you do not use Steam Families — it is opt-in.

5. Avoid the host-migration crash

If borderlands 4 coop disconnects always happen after a party wipe, the host is hitting the migration crash. Workaround until patch 1.5:

After a wipe, do NOT immediately restart the encounter.
Wait 10 seconds at the death screen for state to settle.
Have the host quit to main menu and re-host the session, rather than migrating.

If the host has the worst connection, transfer the host role manually before the encounter:

In-game social menu -> Right-click your name -> Make Host

Skip if you have never seen a crash on host migration — the bug is rare on stable hosts.

Did this guide fix your issue?

FAQ

  • Why do borderlands 4 coop disconnects happen only with one specific friend? The two of you have incompatible NAT types. If both are Strict, neither can punch through. One of you needs UPnP or manual port forwarding.
  • Does using a VPN help with co-op? Sometimes. A VPN with UDP support and consistent routing can bypass ISP-level CGNAT. Steam works best with VPNs that expose IPv4 directly.
  • Will the patch 1.5 PTR fix this? Patch 1.5 PTR notes mention “improved host migration stability” and “Steam Family presence sync” — both should help. We will retest when 1.5 ships.
  • Can I play co-op via Steam Remote Play instead? Yes, and it bypasses NAT entirely. Quality drops on busy fights but it is a workable fallback for one-off sessions.