@Chriscox86 

Hi, May I know the model number of your mobile phone? Is your smartphone the only device that had experienced this issue?

After "either rebooting my phone or reconnecting to the network", would the same issue start again when you are at home?

Here are some suggestions for your reference:

1. Turn off "mesh technology" for the smartphone on the Deco APP.

2. Enable the guest network for 5ghz only and check whether the mobile phone could automatically reconnect to the guest 5ghz and have internet service.

Wait for your reply.

Best regards.

  @Chriscox86 

Hi, you could refer to this link to find the "Mesh Technology". There is a separate switch on each mobile device, so it will not affect the network performance on other devices.

It is also suggested to turn off "fast roaming" temporarily just for troubleshooting purposes.

https://community.tp-link.com/en/home/kb/detail/412552 (case 3)

 And as for galaxy s21 ultra, I also wish you could check with Samsung support to see if there is any new version since I googled around and there were several similar feedback with different brands of mesh WiFi.

Best regards.