Hi  @Kaalz 

Please follow these steps to troubleshoot:
1. Check Cable and Connections:
    1)Use a high-quality Ethernet cable (Cat6 or higher).
    2)Ensure secure connections to the EAP and network device. (e.g., switch, router).
2. Check Port Configuration:
    1)Log in to the EAP's web interface and set LAN port to Auto Negotiation.
    2)Modify specific settings related to LAN port speed if needed.
3. Test with Different Devices:
    Connect the EAP access point to different devices (e.g., a laptop, desktop computer) to identify the source of the issue. 

For your case, you may swap the cable's of 100mbps EAP and 1000mbps EAP, and see if the issue comes with the EAP units or the cables.

4. Update Firmware:
    Ensure the EAP runs the latest firmware. Install updates from TP-Link's website.
5. Factory Reset:
    Reset the EAP to default settings if issues persist (backup configurations first). Remember to back up any important configurations before doing this.