diff --git a/README.md b/README.md
index a347fda..7d1f845 100644
--- a/README.md
+++ b/README.md
@@ -162,9 +162,23 @@ Gruppen sind über die API abrufbar:
 - `GET /api/groups/{id}/members` — Nur Members einer Gruppe
 - `GET /api/contacts/{id}` — Enthält `groups`-Feld mit Gruppennamen
 
-Wird ein Kontakt gelöscht, wird die Mitgliedschaft in Gruppen
-automatisch entfernt (`ON DELETE CASCADE`). Die Gruppe selbst bleibt
-erhalten.
+Wird eine Gruppe gelöscht, werden zugehörige Memberschaften automatisch
+entfernt (`ON DELETE CASCADE`). Gelöschte Mitglied-Kontakte verbleiben
+als Member-Eintrag in der Gruppe (ohne aufgelöste Kontaktdaten). Beim
+nächsten vollen Re-Sync werden tote Memberschaften bereinigt.
+
+### Migration bei erstem Deploy
+
+Bei Bestands-DBs lagen Gruppen bisher als normale Kontakte in der
+`contacts`-Tabelle. Nach dem Deploy müssen diese einmalig bereinigt
+werden:
+
+1. Sync-Container stoppen: `docker compose stop icloud-contacts-sync`
+2. Sync-State zurücksetzen: `DELETE FROM sync_state;` (erzwingt vollen Re-Sync)
+3. Container neu starten: `docker compose start icloud-contacts-sync`
+
+Beim nächsten Sync-Lauf werden alle vCards neu klassifiziziert —
+Gruppen landen in `groups`, Kontakte bleiben in `contacts`.
 
 ## 11. Web-Ansicht und API (interner Zugriff über Authelia)
 
diff --git a/sql/schema.sql b/sql/schema.sql
index b92e134..2a1ffac 100644
--- a/sql/schema.sql
+++ b/sql/schema.sql
@@ -77,7 +77,8 @@ CREATE TABLE IF NOT EXISTS group_members (
     group_id    INT NOT NULL,
     member_uid  VARCHAR(255) NOT NULL,
     FOREIGN KEY (group_id) REFERENCES `groups`(id) ON DELETE CASCADE,
-    UNIQUE KEY uq_group_member (group_id, member_uid)
+    UNIQUE KEY uq_group_member (group_id, member_uid),
+    KEY idx_group_members_member_uid (member_uid)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
 
 -- Protokoll der Geburtstags-Mails, verhindert Doppelversand am selben Tag.
diff --git a/src/api/main.py b/src/api/main.py
index a0c6d25..83d201f 100644
--- a/src/api/main.py
+++ b/src/api/main.py
@@ -215,12 +215,11 @@ def list_sync_runs(current_user: str = Depends(get_current_user)):
 
 @app.get("/api/groups", response_model=GroupListResponse)
 def list_groups(
-    request: Request,
     limit: int = Query(default=50, le=200),
     offset: int = Query(default=0, ge=0),
     current_user: str = Depends(get_current_user),
 ):
-    account_name, is_admin = resolve_account_for_user(current_user)
+    account_name, _ = resolve_account_for_user(current_user)
 
     with db.get_connection() as conn:
         where_clause, params = _account_filter_clause(account_name)
@@ -245,7 +244,7 @@ def list_groups(
 
 @app.get("/api/groups/{group_id}", response_model=GroupDetailOut)
 def get_group(group_id: int, current_user: str = Depends(get_current_user)):
-    account_name, is_admin = resolve_account_for_user(current_user)
+    account_name, _ = resolve_account_for_user(current_user)
 
     with db.get_connection() as conn:
         where_clause, params = _account_filter_clause(account_name)
@@ -265,9 +264,9 @@ def get_group(group_id: int, current_user: str = Depends(get_current_user)):
             cur.execute(
                 """SELECT gm.member_uid, c.id, c.full_name, c.given_name, c.family_name
                    FROM group_members gm
+                   JOIN `groups` g ON g.id = gm.group_id
                    LEFT JOIN contacts c ON c.account = g.account AND c.uid = gm.member_uid
-                   CROSS JOIN `groups` g
-                   WHERE g.id = %s AND gm.group_id = g.id""",
+                   WHERE g.id = %s""",
                 (group_id,),
             )
             members = cur.fetchall()
@@ -286,24 +285,26 @@ def get_group(group_id: int, current_user: str = Depends(get_current_user)):
 
 @app.get("/api/groups/{group_id}/members")
 def get_group_members(group_id: int, current_user: str = Depends(get_current_user)):
-    account_name, is_admin = resolve_account_for_user(current_user)
+    account_name, _ = resolve_account_for_user(current_user)
 
     with db.get_connection() as conn:
         where_clause, params = _account_filter_clause(account_name)
         with conn.cursor() as cur:
             cur.execute(
-                f"""SELECT g.id FROM `groups` g {where_clause}
+                f"""SELECT g.id, g.account FROM `groups` g {where_clause}
                     {"AND" if where_clause else "WHERE"} g.id = %s""",
                 params + [group_id],
             )
-            if not cur.fetchone():
+            group = cur.fetchone()
+            if not group:
                 return {}
 
             cur.execute(
                 """SELECT gm.member_uid, c.id, c.full_name, c.given_name, c.family_name,
                           c.organization, c.birthday, c.photo_url
                    FROM group_members gm
-                   LEFT JOIN contacts c ON c.uid = gm.member_uid
+                   JOIN `groups` g ON g.id = gm.group_id
+                   LEFT JOIN contacts c ON c.account = g.account AND c.uid = gm.member_uid
                    WHERE gm.group_id = %s""",
                 (group_id,),
             )
diff --git a/src/vcard_parser.py b/src/vcard_parser.py
index 03fe680..7842aad 100644
--- a/src/vcard_parser.py
+++ b/src/vcard_parser.py
@@ -61,10 +61,6 @@ def parse_group(raw_text: str, account: str, etag: str | None = None) -> dict |
         else:
             member_uids.append(value)
 
-    if not member_uids:
-        logger.debug("Gruppe %s hat keine Members, überspringe", uid)
-        return None
-
     return {
         "account": account,
         "uid": uid,