Hi Bruna,
Greetings from Syncfusion.
Thank you for sharing your sample. We ran the sample and found that it works perfectly fine, with no noticeable delays during initial load or expand/collapse actions (refer to the attached screenshot & video).
To assist you further, could you please provide the following details:
Delay Time Details: Share the specific delay times you are experiencing for expand/collapse actions.
Other Performance Issues: Let us know if there are any other areas where you are experiencing delays or performance issues.
Video demo: Share us your issue replicating video demostration.
Once we have this information, we can investigate further and provide tailored recommendations to improve performance.

Regards,
Sridharan
Attachment:
Performace_6caf747c.zip