diff --git a/apps/login/src/lib/server/loginname.ts b/apps/login/src/lib/server/loginname.ts
index c0c726820..a54468963 100644
--- a/apps/login/src/lib/server/loginname.ts
+++ b/apps/login/src/lib/server/loginname.ts
@@ -1,5 +1,6 @@
 "use server";
 
+import * as Sentry from "@sentry/nextjs";
 import { create } from "@zitadel/client";
 import { ChecksSchema } from "@zitadel/proto/zitadel/session/v2/session_service_pb";
 import { AuthenticationMethodType } from "@zitadel/proto/zitadel/user/v2/user_service_pb";
@@ -219,6 +220,22 @@ export async function sendLoginname(command: SendLoginnameCommand) {
       userLoginSettings?.disableLoginWithPhone
     ) {
       if (user.preferredLoginName !== concatLoginname) {
+        Sentry.captureMessage("User not found: IDP-only validation failed", {
+          level: "error",
+          tags: {
+            validation_type: "idp_only",
+            user_id: user.userId,
+          },
+          extra: {
+            preferredLoginName: user.preferredLoginName,
+            concatLoginname,
+            commandLoginName: command.loginName,
+            email: humanUser?.email?.email,
+            organizationId: command.organization,
+            disableLoginWithEmail: userLoginSettings?.disableLoginWithEmail,
+            disableLoginWithPhone: userLoginSettings?.disableLoginWithPhone,
+          },
+        });
         return { error: "User not found in the system!" };
       }
     } else if (userLoginSettings?.disableLoginWithEmail) {
@@ -226,6 +243,25 @@ export async function sendLoginname(command: SendLoginnameCommand) {
         user.preferredLoginName !== concatLoginname ||
         humanUser?.phone?.phone !== command.loginName
       ) {
+        Sentry.captureMessage(
+          "User not found: email-disabled validation failed",
+          {
+            level: "error",
+            tags: {
+              validation_type: "email_disabled",
+              user_id: user.userId,
+            },
+            extra: {
+              preferredLoginName: user.preferredLoginName,
+              concatLoginname,
+              commandLoginName: command.loginName,
+              phone: humanUser?.phone?.phone,
+              organizationId: command.organization,
+              disableLoginWithEmail: userLoginSettings?.disableLoginWithEmail,
+              disableLoginWithPhone: userLoginSettings?.disableLoginWithPhone,
+            },
+          },
+        );
         return { error: "User not found in the system!" };
       }
     } else if (userLoginSettings?.disableLoginWithPhone) {
@@ -233,6 +269,25 @@ export async function sendLoginname(command: SendLoginnameCommand) {
         user.preferredLoginName !== concatLoginname ||
         humanUser?.email?.email !== command.loginName
       ) {
+        Sentry.captureMessage(
+          "User not found: phone-disabled validation failed",
+          {
+            level: "error",
+            tags: {
+              validation_type: "phone_disabled",
+              user_id: user.userId,
+            },
+            extra: {
+              preferredLoginName: user.preferredLoginName,
+              concatLoginname,
+              commandLoginName: command.loginName,
+              email: humanUser?.email?.email,
+              organizationId: command.organization,
+              disableLoginWithEmail: userLoginSettings?.disableLoginWithEmail,
+              disableLoginWithPhone: userLoginSettings?.disableLoginWithPhone,
+            },
+          },
+        );
         return { error: "User not found in the system!" };
       }
     }
diff --git a/apps/login/src/lib/zitadel.ts b/apps/login/src/lib/zitadel.ts
index 727495cd2..45a0409c2 100644
--- a/apps/login/src/lib/zitadel.ts
+++ b/apps/login/src/lib/zitadel.ts
@@ -1,3 +1,4 @@
+import * as Sentry from "@sentry/nextjs";
 import { Client, create, Duration } from "@zitadel/client";
 import { createServerTransport as libCreateServerTransport } from "@zitadel/client/node";
 import { makeReqCtx } from "@zitadel/client/v2";
@@ -856,6 +857,18 @@ export async function searchUsers({
   }
 
   if (loginNameResult.result.length > 1) {
+    Sentry.captureMessage("Multiple users found: loginName search", {
+      level: "error",
+      tags: {
+        search_type: "multiple_users_loginname",
+      },
+      extra: {
+        searchValue,
+        organizationId,
+        suffix,
+        resultCount: loginNameResult.result.length,
+      },
+    });
     return { error: "Multiple users found" };
   }
 
@@ -951,6 +964,21 @@ export async function searchUsers({
   }
 
   if (emailOrPhoneResult.result.length > 1) {
+    Sentry.captureMessage("Multiple users found: email/phone search", {
+      level: "error",
+      tags: {
+        search_type: "multiple_users_email_phone",
+      },
+      extra: {
+        searchValue,
+        organizationId,
+        suffix,
+        userId,
+        resultCount: emailOrPhoneResult.result.length,
+        disableLoginWithEmail: loginSettings?.disableLoginWithEmail,
+        disableLoginWithPhone: loginSettings?.disableLoginWithPhone,
+      },
+    });
     return { error: "Multiple users found." };
   }
 
@@ -958,6 +986,23 @@ export async function searchUsers({
     return emailOrPhoneResult;
   }
 
+  Sentry.captureMessage("User not found: searchUsers exhausted all queries", {
+    level: "error",
+    tags: {
+      search_type: "user_search_failed",
+    },
+    extra: {
+      searchValue,
+      organizationId,
+      suffix,
+      userId,
+      disableLoginWithEmail: loginSettings?.disableLoginWithEmail,
+      disableLoginWithPhone: loginSettings?.disableLoginWithPhone,
+      loginNameResultCount: 0,
+      emailOrPhoneResultCount: emailOrPhoneResult.result.length,
+    },
+  });
+
   return { error: "User not found in the system" };
 }