docs: update sdk doc with note on using multiple instances (#6311)

docs/reference/sdk.md

@@ -68,6 +68,27 @@ The storage implementation. See [Storage](#storage) for more information.
 
 Defaults to an instance of `MemoryStorage` when in node.js, and `LocalStorage` when in browsers.
 
+**NOTE:** 
+
+If you plan to use multiple SDK instances at once, keep in mind that they will share the Storage across them, leading to unpredictable behaviors. This scenario might be a case while writing tests.
+
+For example, the SDK instance that executed last the `login()` method writes the resulting `access_token` into the Storage and **overwrites** any prior fetched `access_token` from any other SDK instance. That might mix up your test scenario by granting false access rights to your previous logged-in users.
+
+Adding prefixes to your Storage instances would solve this error:
+
+```js
+import { Directus, MemoryStorage } from "@directus/sdk";
+import { randomBytes } from "crypto";
+
+// ...
+
+const prefix = randomBytes(8).toString("hex");
+const storage = new MemoryStorage(prefix);
+const url = `http://${host}:${port}`;
+const directus = new Directus(url, { storage });
+
+```
+
 #### `options.transport`
 
 The transport implementation. See [Transport](#transport) for more information.