diff --git a/src/database/migrations/0020_quiz_generated_for_cascade.sql b/src/database/migrations/0020_quiz_generated_for_cascade.sql
new file mode 100644
index 0000000..b208b41
--- /dev/null
+++ b/src/database/migrations/0020_quiz_generated_for_cascade.sql
@@ -0,0 +1,10 @@
+-- Drop existing constraint
+ALTER TABLE quizzes 
+DROP CONSTRAINT IF EXISTS quizzes_generated_for_users_id_fk;
+
+-- Recreate with CASCADE
+ALTER TABLE quizzes 
+ADD CONSTRAINT quizzes_generated_for_users_id_fk 
+FOREIGN KEY (generated_for) 
+REFERENCES users(id) 
+ON DELETE CASCADE;
diff --git a/src/database/schema.ts b/src/database/schema.ts
index 3ef8ee0..18f46d7 100644
--- a/src/database/schema.ts
+++ b/src/database/schema.ts
@@ -178,7 +178,9 @@ export const quizzes = pgTable(
       .references(() => courses.id, { onDelete: "cascade" }),
     moduleId: varchar("module_id", { length: 100 }).notNull(),
     questions: jsonb("questions").notNull(),
-    generatedFor: uuid("generated_for").references(() => users.id),
+    generatedFor: uuid("generated_for").references(() => users.id, {
+      onDelete: "cascade",
+    }),
     createdAt: timestamp("created_at", { withTimezone: true })
       .notNull()
       .defaultNow(),
diff --git a/src/modules/rewards/reward.service.ts b/src/modules/rewards/reward.service.ts
index 8eec5b7..e74ccfd 100644
--- a/src/modules/rewards/reward.service.ts
+++ b/src/modules/rewards/reward.service.ts
@@ -48,6 +48,28 @@ const REWARD_AMOUNT = 10; // credits per passed quiz
 const PENDING_REWARDS_TTL_SECONDS = 10; // #327 — near-real-time
 const PENDING_CONFIRMATION_ETA_SECONDS = 300; // reconcile job runs every 5 min
 
+/**
+ * Detects if an error is a bad sequence error from Stellar.
+ * Uses multiple detection methods for robustness across SDK versions.
+ */
+function isBadSeqError(err: StellarError): boolean {
+  // Primary detection: string matching (backwards compatible)
+  if (err.message.includes("bad_seq") || err.message.includes("tx_bad_seq")) {
+    return true;
+  }
+  
+  // Robust detection: check Horizon response structure
+  const response = (err as any)?.response;
+  if (response?.status === 400) {
+    const resultCodes = response?.data?.extras?.result_codes;
+    if (resultCodes?.transaction === "tx_bad_seq") {
+      return true;
+    }
+  }
+  
+  return false;
+}
+
 export async function selectSubmissionForUpdate(
   tx: Parameters<typeof db.transaction>[0] extends (arg: infer T) => any ? T : never,
   submissionId: string,
@@ -122,7 +144,7 @@ async function _executeStellarRewardClaim(claimData: RewardClaimData): Promise<s
     );
     if (
       err instanceof StellarError &&
-      (err.message.includes("bad_seq") || err.message.includes("tx_bad_seq"))
+      isBadSeqError(err)
     ) {
       return handleBadSeqError(claimData.submissionId, claimData.stellarAddress);
     }
@@ -229,7 +251,7 @@ export async function processRewardClaim(
     await _applyRewardToDb(submissionId, userId, txHash);
 
     return true;
-  }).then(async (result) => {
+  }, 90_000).then(async (result) => {
     if (result) {
       await cacheDel(cacheKey("user", "progress", userId));
       await cacheDel(cacheKey("user", "profile", userId));
@@ -418,7 +440,7 @@ export class RewardService {
         queued: false,
         message: `Successfully claimed ${REWARD_AMOUNT} credits`,
       };
-    });
+    }, 90_000);
   }
 
   /**
@@ -482,7 +504,7 @@ export class RewardService {
     }));
 
     const result = { history, total: totalResult?.value ?? 0 };
-    await cacheSet(cacheKeyString, result, 30);
+    await cacheSet(cacheKeyString, result, 300);
 
     return result;
   }
diff --git a/src/stellar/transactions.ts b/src/stellar/transactions.ts
index 0d16cb5..f439a92 100644
--- a/src/stellar/transactions.ts
+++ b/src/stellar/transactions.ts
@@ -14,6 +14,28 @@ import { withAccountLock } from "../utils/account-lock.js";
 
 const MAX_SEQ_RETRIES = 3;
 
+/**
+ * Detects if an error is a bad sequence error from Stellar.
+ * Uses multiple detection methods for robustness across SDK versions.
+ */
+function isBadSeqError(err: StellarError): boolean {
+  // Primary detection: string matching (backwards compatible)
+  if (err.message.includes("bad_seq") || err.message.includes("tx_bad_seq")) {
+    return true;
+  }
+  
+  // Robust detection: check Horizon response structure
+  const response = (err as any)?.response;
+  if (response?.status === 400) {
+    const resultCodes = response?.data?.extras?.result_codes;
+    if (resultCodes?.transaction === "tx_bad_seq") {
+      return true;
+    }
+  }
+  
+  return false;
+}
+
 /**
  * Build and submit a Soroban contract invocation transaction.
  */
@@ -81,7 +103,7 @@ export async function invokeContract(
         const result = await stellarClient.submitTransaction(preparedTx);
         return result.hash;
       } catch (err: any) {
-        if (err instanceof StellarError && (err.message.includes("bad_seq") || err.message.includes("tx_bad_seq"))) {
+        if (err instanceof StellarError && isBadSeqError(err)) {
           await sequenceCache.invalidate(keypair.publicKey());
           logger.warn({ attempt, err }, "Sequence number conflict, retrying with fresh sequence");
           continue;
diff --git a/src/utils/lock.ts b/src/utils/lock.ts
index 2996f45..be58626 100644
--- a/src/utils/lock.ts
+++ b/src/utils/lock.ts
@@ -6,7 +6,7 @@ import { logger } from "./logger.js";
 export async function withLock<T>(
   key: string,
   fn: () => Promise<T>,
-  ttlMs: number = 30_000
+  ttlMs: number = 60_000
 ): Promise<T> {
   const lockKey = `lock:${key}`;
   const lockValue = crypto.randomUUID();