@stevewG
Hi, Sorry for the delay.
Can you help me run the following test:
1. power off the reset two satellite Deco unit and leave the main Deco only;
2. turn off the 2.4ghz temporarily;
3. connect the Samsung A8 and A12 to the Wi-Fi again to test the speed;
Note: Please try to change different speedtest servers when running the speedtest;
4.Please refer to this link to check the link speed as well:
https://www.tp-link.com/support/faq/2265/
Please send us the speed test pictures and the screen-shot of the link speed so that we could forward your case to the senior engineers later;
Thank you very much.