diff --git a/clientapi/routing/sendevent.go b/clientapi/routing/sendevent.go
index fc9c05ba9..69131966b 100644
--- a/clientapi/routing/sendevent.go
+++ b/clientapi/routing/sendevent.go
@@ -263,7 +263,11 @@ func SendEvent(
 }
 
 func updatePowerLevels(req *http.Request, r map[string]interface{}, roomID string, rsAPI api.ClientRoomserverAPI) error {
-	userMap := r["users"].(map[string]interface{})
+	users, ok := r["users"]
+	if !ok {
+		return nil
+	}
+	userMap := users.(map[string]interface{})
 	validRoomID, err := spec.NewRoomID(roomID)
 	if err != nil {
 		return err
@@ -277,7 +281,8 @@ func updatePowerLevels(req *http.Request, r map[string]interface{}, roomID strin
 		if err != nil {
 			return err
 		} else if senderID == nil {
-			return fmt.Errorf("sender ID not found for %s in %s", uID, *validRoomID)
+			util.GetLogger(req.Context()).Warnf("sender ID not found for %s in %s", uID, *validRoomID)
+			continue
 		}
 		userMap[string(*senderID)] = level
 		delete(userMap, user)
diff --git a/roomserver/internal/perform/perform_leave.go b/roomserver/internal/perform/perform_leave.go
index 5c63a6684..5bea00445 100644
--- a/roomserver/internal/perform/perform_leave.go
+++ b/roomserver/internal/perform/perform_leave.go
@@ -93,11 +93,21 @@ func (r *Leaver) performLeaveRoomByID(
 	isInvitePending, senderUser, eventID, _, err := helpers.IsInvitePending(ctx, r.DB, req.RoomID, *leaver)
 	if err == nil && isInvitePending {
 		sender, serr := r.RSAPI.QueryUserIDForSender(ctx, *roomID, senderUser)
-		if serr != nil || sender == nil {
-			return nil, fmt.Errorf("sender %q has no matching userID", senderUser)
+		if serr != nil {
+			return nil, fmt.Errorf("failed looking up userID for sender %q: %w", senderUser, serr)
 		}
-		if !r.Cfg.Matrix.IsLocalServerName(sender.Domain()) {
-			return r.performFederatedRejectInvite(ctx, req, res, *sender, eventID, *leaver)
+
+		var domain spec.ServerName
+		if sender == nil {
+			// TODO: Currently a federated invite has no way of knowing the mxid_mapping of the inviter.
+			// Should we add the inviter's m.room.member event (with mxid_mapping) to invite_room_state to allow
+			// the invited user to leave via the inviter's server?
+			domain = roomID.Domain()
+		} else {
+			domain = sender.Domain()
+		}
+		if !r.Cfg.Matrix.IsLocalServerName(domain) {
+			return r.performFederatedRejectInvite(ctx, req, res, domain, eventID, *leaver)
 		}
 		// check that this is not a "server notice room"
 		accData := &userapi.QueryAccountDataResponse{}
@@ -219,14 +229,14 @@ func (r *Leaver) performFederatedRejectInvite(
 	ctx context.Context,
 	req *api.PerformLeaveRequest,
 	res *api.PerformLeaveResponse, // nolint:unparam
-	inviteSender spec.UserID, eventID string,
+	inviteDomain spec.ServerName, eventID string,
 	leaver spec.SenderID,
 ) ([]api.OutputEvent, error) {
 	// Ask the federation sender to perform a federated leave for us.
 	leaveReq := fsAPI.PerformLeaveRequest{
 		RoomID:      req.RoomID,
 		UserID:      req.Leaver.String(),
-		ServerNames: []spec.ServerName{inviteSender.Domain()},
+		ServerNames: []spec.ServerName{inviteDomain},
 	}
 	leaveRes := fsAPI.PerformLeaveResponse{}
 	if err := r.FSAPI.PerformLeave(ctx, &leaveReq, &leaveRes); err != nil {
diff --git a/setup/config/config_roomserver.go b/setup/config/config_roomserver.go
index 06e7757fb..f47803f48 100644
--- a/setup/config/config_roomserver.go
+++ b/setup/config/config_roomserver.go
@@ -16,7 +16,8 @@ type RoomServer struct {
 }
 
 func (c *RoomServer) Defaults(opts DefaultOpts) {
-	c.DefaultRoomVersion = gomatrixserverlib.RoomVersionV10
+	//c.DefaultRoomVersion = gomatrixserverlib.RoomVersionV10
+	c.DefaultRoomVersion = gomatrixserverlib.RoomVersionPseudoIDs
 	if opts.Generate {
 		if !opts.SingleDatabase {
 			c.Database.ConnectionString = "file:roomserver.db"
diff --git a/syncapi/synctypes/clientevent.go b/syncapi/synctypes/clientevent.go
index 6812f8332..736c760a9 100644
--- a/syncapi/synctypes/clientevent.go
+++ b/syncapi/synctypes/clientevent.go
@@ -363,14 +363,17 @@ func updatePowerLevelEvent(userIDForSender spec.UserIDForSender, se gomatrixserv
 		}
 		newPls[user] = level
 	}
-	var newPlBytes, newEv []byte
-	newPlBytes, err = json.Marshal(newPls)
-	if err != nil {
-		return nil, err
-	}
-	newEv, err = sjson.SetRawBytes(se.JSON(), "content.users", newPlBytes)
-	if err != nil {
-		return nil, err
+	var newPlBytes []byte
+	newEv := se.JSON()
+	if len(pls.Users) > 0 {
+		newPlBytes, err = json.Marshal(newPls)
+		if err != nil {
+			return nil, err
+		}
+		newEv, err = sjson.SetRawBytes(se.JSON(), "content.users", newPlBytes)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	// do the same for prev content
@@ -401,13 +404,15 @@ func updatePowerLevelEvent(userIDForSender spec.UserIDForSender, se gomatrixserv
 		}
 		newPls[user] = level
 	}
-	newPlBytes, err = json.Marshal(newPls)
-	if err != nil {
-		return nil, err
-	}
-	newEv, err = sjson.SetRawBytes(newEv, "unsigned.prev_content.users", newPlBytes)
-	if err != nil {
-		return nil, err
+	if len(pls.Users) > 0 {
+		newPlBytes, err = json.Marshal(newPls)
+		if err != nil {
+			return nil, err
+		}
+		newEv, err = sjson.SetRawBytes(newEv, "unsigned.prev_content.users", newPlBytes)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	var evNew gomatrixserverlib.PDU