diff --git a/internal/web/service/client_bulk.go b/internal/web/service/client_bulk.go
index e3305c8d2..81daa1346 100644
--- a/internal/web/service/client_bulk.go
+++ b/internal/web/service/client_bulk.go
@@ -1208,7 +1208,7 @@ func (s *ClientService) BulkCreate(inboundSvc *InboundService, payloads []Client
 
 	db := database.GetDB()
 	const lookupChunk = 400
-	existingEmailSub := make(map[string]string, len(emails))
+	existingByEmail := make(map[string]model.ClientRecord, len(emails))
 	for start := 0; start < len(emails); start += lookupChunk {
 		end := min(start+lookupChunk, len(emails))
 		var rows []model.ClientRecord
@@ -1216,7 +1216,7 @@ func (s *ClientService) BulkCreate(inboundSvc *InboundService, payloads []Client
 			return result, false, e
 		}
 		for i := range rows {
-			existingEmailSub[strings.ToLower(rows[i].Email)] = rows[i].SubID
+			existingByEmail[strings.ToLower(rows[i].Email)] = rows[i]
 		}
 	}
 	existingSubOwner := make(map[string]string, len(subIDs))
@@ -1252,10 +1252,24 @@ func (s *ClientService) BulkCreate(inboundSvc *InboundService, payloads []Client
 
 	for idx := range prep {
 		le := strings.ToLower(prep[idx].client.Email)
-		if existSub, ok := existingEmailSub[le]; ok && existSub != prep[idx].client.SubID {
-			failed[idx] = true
-			reason[idx] = "email already in use: " + prep[idx].client.Email
-			continue
+		if rec, ok := existingByEmail[le]; ok {
+			if rec.SubID != prep[idx].client.SubID {
+				failed[idx] = true
+				reason[idx] = "email already in use: " + prep[idx].client.Email
+				continue
+			}
+			if prep[idx].client.ID == "" {
+				prep[idx].client.ID = rec.UUID
+			}
+			if prep[idx].client.Password == "" {
+				prep[idx].client.Password = rec.Password
+			}
+			if prep[idx].client.Auth == "" {
+				prep[idx].client.Auth = rec.Auth
+			}
+			if prep[idx].client.Secret == "" {
+				prep[idx].client.Secret = rec.Secret
+			}
 		}
 		if owner, ok := existingSubOwner[prep[idx].client.SubID]; ok && owner != le {
 			failed[idx] = true
diff --git a/internal/web/service/client_create_reuse_test.go b/internal/web/service/client_create_reuse_test.go
new file mode 100644
index 000000000..c889961f5
--- /dev/null
+++ b/internal/web/service/client_create_reuse_test.go
@@ -0,0 +1,54 @@
+package service
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
+)
+
+func settingsHoldUUID(t *testing.T, inboundSvc *InboundService, inboundId int, uuid string) bool {
+	t.Helper()
+	ib, err := inboundSvc.GetInbound(inboundId)
+	if err != nil {
+		t.Fatalf("GetInbound %d: %v", inboundId, err)
+	}
+	return strings.Contains(ib.Settings, uuid)
+}
+
+func TestCreateRepeatKeepsExistingUUID(t *testing.T) {
+	setupBulkDB(t)
+	svc := &ClientService{}
+	inboundSvc := &InboundService{}
+
+	ibA := mkInbound(t, 21001, model.VLESS, `{"clients":[]}`)
+	ibB := mkInbound(t, 21002, model.VLESS, `{"clients":[]}`)
+
+	const originalUUID = "aaaaaaaa-1111-2222-3333-444444444444"
+	if _, err := svc.Create(inboundSvc, &ClientCreatePayload{
+		Client:     model.Client{Email: "repeat@x", ID: originalUUID, SubID: "sub-repeat", Enable: true},
+		InboundIds: []int{ibA.Id},
+	}); err != nil {
+		t.Fatalf("first Create: %v", err)
+	}
+	if rec := lookupClientRecord(t, "repeat@x"); rec.UUID != originalUUID {
+		t.Fatalf("record UUID after first Create = %q, want %q", rec.UUID, originalUUID)
+	}
+
+	if _, err := svc.Create(inboundSvc, &ClientCreatePayload{
+		Client:     model.Client{Email: "repeat@x", SubID: "sub-repeat", Enable: true},
+		InboundIds: []int{ibB.Id},
+	}); err != nil {
+		t.Fatalf("repeat Create: %v", err)
+	}
+
+	if rec := lookupClientRecord(t, "repeat@x"); rec.UUID != originalUUID {
+		t.Fatalf("record UUID after repeat Create = %q, want %q", rec.UUID, originalUUID)
+	}
+	if !settingsHoldUUID(t, inboundSvc, ibA.Id, originalUUID) {
+		t.Fatalf("inbound A settings lost the original UUID")
+	}
+	if !settingsHoldUUID(t, inboundSvc, ibB.Id, originalUUID) {
+		t.Fatalf("inbound B settings did not reuse the original UUID")
+	}
+}
diff --git a/internal/web/service/client_crud.go b/internal/web/service/client_crud.go
index dc36d9d2a..2bca49d7e 100644
--- a/internal/web/service/client_crud.go
+++ b/internal/web/service/client_crud.go
@@ -82,6 +82,20 @@ func (s *ClientService) Create(inboundSvc *InboundService, payload *ClientCreate
 		if existing.SubID == "" || existing.SubID != client.SubID {
 			return false, common.NewError("email already in use:", client.Email)
 		}
+		// Reuse stored credentials when re-adding an existing identity, or
+		// fillProtocolDefaults mints a fresh UUID that desyncs other inbounds.
+		if client.ID == "" {
+			client.ID = existing.UUID
+		}
+		if client.Password == "" {
+			client.Password = existing.Password
+		}
+		if client.Auth == "" {
+			client.Auth = existing.Auth
+		}
+		if client.Secret == "" {
+			client.Secret = existing.Secret
+		}
 	}
 
 	if client.SubID != "" {
@@ -345,6 +359,9 @@ func (s *ClientService) Update(inboundSvc *InboundService, id int, updated model
 	if updated.Auth == "" {
 		updated.Auth = existing.Auth
 	}
+	if updated.Secret == "" {
+		updated.Secret = existing.Secret
+	}
 
 	if updated.Email != existing.Email {
 		var collisionCount int64