diff --git a/apps/api/src/player/player.service.ts b/apps/api/src/player/player.service.ts
index 6bc9d8953..91059f65c 100644
--- a/apps/api/src/player/player.service.ts
+++ b/apps/api/src/player/player.service.ts
@@ -11,6 +11,7 @@ import {
   type Circular,
   type Flatten,
   flatten,
+  unflatten,
 } from "@statsify/util";
 import { CacheLevel, StatusNotFoundException } from "@statsify/api-client";
 import { HypixelService } from "#hypixel";
@@ -176,8 +177,11 @@ export class PlayerService {
     const serializedPlayer = serialize<Player>(Player, flatPlayer);
 
     const promises = [
+      // Thousands of dotted keys make Mongoose's change tracking O(n²)
       this.playerModel
-        .replaceOne({ uuid: player.uuid }, serializedPlayer, { upsert: true })
+        .replaceOne({ uuid: player.uuid }, unflatten(serializedPlayer), {
+          upsert: true,
+        })
         .exec(),
       this.playerLeaderboardService.addLeaderboards(
         Player,
diff --git a/apps/api/src/session/session.service.ts b/apps/api/src/session/session.service.ts
index 0675b3826..2c38c93ba 100644
--- a/apps/api/src/session/session.service.ts
+++ b/apps/api/src/session/session.service.ts
@@ -11,7 +11,7 @@ import {
   PlayerNotFoundException,
   SessionNotFoundException,
 } from "@statsify/api-client";
-import { type Circular, flatten } from "@statsify/util";
+import { type Circular, flatten, unflatten } from "@statsify/util";
 import { DateTime } from "luxon";
 import {
   Inject,
@@ -59,7 +59,7 @@ export class SessionService {
 
     const doc = serialize(Player, flatPlayer);
 
-    await this.sessionModel.replaceOne({ uuid: doc.uuid }, doc, { upsert: true }).lean().exec();
+    await this.sessionModel.replaceOne({ uuid: doc.uuid }, unflatten(doc), { upsert: true }).lean().exec();
 
     return deserialize(Player, flatPlayer);
   }