What is Photon host migration?

When the master client disconnects from a Photon room, Photon promotes another peer to master. Your game receives On master client changed. If you don’t handle this, owned objects (NPCs, spawned items) lose their authoritative source.

How do I re-sync ownership after migration?

On master client changed, the new master takes ownership of any orphaned objects. Iterate game objects and reassign authority. Listeners on the other clients update their object IDs to match the new master’s broadcasts.

What happens to in-flight RPCs during migration?

Lost. Photon doesn’t replay events through migration. For critical state (scores, item pickups), use Custom Properties on the room which Photon persists; ad-hoc RPCs are lossy.

Fix: Construct 3 Multiplayer Photon Host Migration Stuck

Quick answer: Listen for On master client changed. On the new master, re-take authority of orphaned objects. Have clients refresh their authority references for spawned actors.

A 4-player multiplayer match. The host crashes. Photon promotes player 2 to master. The other three players see frozen NPCs — the spawned enemies lose their controlling client and stop ticking. Restarting the match resolves it; mid-match recovery doesn’t work.

Master Client Authority Model

In Photon’s model, one peer is master client. Authoritative state (NPC AI, world events) typically runs on the master. When the master leaves:

Photon detects the disconnect.
Promotes another peer to master.
Broadcasts On master client changed to all peers.

Owned objects (those tagged with the old master’s ID) need explicit reassignment.

The Fix

On Photon master client changed:
    If Photon.IsMaster:
        // I’m the new master. Take ownership of orphaned objects.
        For each NPC:
            If NPC.OwnerID = Photon.PreviousMasterID:
                NPC Set OwnerID to Photon.LocalID
        Broadcast "AuthorityHandoff" with data {oldMaster: ..., newMaster: ...}

  On Photon message "AuthorityHandoff":
    For each NPC:
        If NPC.OwnerID = message.oldMaster:
            NPC Set OwnerID to message.newMaster

The new master claims orphans; broadcasts the change; clients update their authority bookkeeping. NPCs resume ticking under the new master’s control.

Persistent State via Room Properties

For state that must survive migration (player scores, current wave number):

Photon Set room property "wave_number" to 5
// Property persists in Photon’s room state; new master reads it on promotion

Photon stores these on its server; migration doesn’t lose them. RPCs and ephemeral messages do get lost.

Detecting Migration

On master client changed includes the previous and new master IDs. Use them to identify orphans precisely — you don’t want to reassign objects owned by other still-active clients.

Verifying

Run a 4-player session. Kill the host (Alt+F4 on the master). Verify the other three players continue playing with NPCs ticking under the new master. Score state should persist (room property); in-flight ephemeral events may be lost (acceptable).

“Photon promotes master client automatically. Your game has to take care of authority handover. Listen for the event and reclaim orphans.”

Use room properties for any state that should outlive a single master — treats Photon as durable storage.