@CR-
These are the things I would check first in such situation:
1. It is possible Deco M4 configuration setting throttles speed. See this document and if it applies to your situation: Using QoS feature of Deco
2. If you are unsure or it did not help, you can disable all Deco speed throttling settings by configuring Deco to run in Access Point mode: How to set up Deco to work in Access Point mode
3. If that has not helped either, configure Main Deco in Deco app to only broadcast on 5GHz, to make sure device you use for speed tests is connected on high speed WiFi network:
![](https://static-community.tp-link.com/other/15/10/2022/9619d83963cf47c7b4981be800a3e401.jpg)
If above didn't fix the problem, review the following document for more suggestions: Troubleshooting: Slow Internet Speed with Deco Devices