@RoyalKin 

Hi, welcome to the community.

Did you run the speedtest when the device is connnected to the Deco X50-5G via Ethernet cable or 5GHz Wi-Fi?

Have you tried to enable the hotspot on the S23 ultra and test how much speed of the mobile hotspot?

It is also suggested to check the Cell ID on the S23 ultra when its speed is nearly 300m/s, then later we could try to manually input the similar Cell ID on the Deco X50-5G,

such as the Cell Lock feature mentioned here:

Thank you very much and best regards.

  @RoyalKin 

Hi, May I know who is your SIM carrier?

Later I'd like to forward your case to the senior engineer for further assistance by email.

Could you please reply my email with the following details?

• A picture of the Internet page on the Deco APP like the picture posted above.
• The model number(or a product link) of your external 5G antennas.
• the 5G Service Cell info on the S23 ultra, such as:How to find the Cell frequency on my Samsung phone

Thank you very much and best regards.

  @RoyalKin 

Hi, Did you receive my email? and how about some screenshots of the "Internet" page of Deco X50-5G on the Deco APP?

Best regards.

  @RoyalKin 

Thank you for the update - that's great news!

It seems like the Deco X50-5G is now selecting the optimal 5G bands and delivering fantastic speeds.

Please monitor the network performance for some time and feel free to share any further improvements here.

Thanks again and wish you a nice weekend in advance.