One device not connecting

[Juniper275]

I bought an iPhone 17 six weeks ago and it connects at a much lower speed than all the other devices in the house. 
I've spent hours on the phone to Apple and all the diagnostics show that there's no

problem with the phone. Just come back from another 'genius' appointment and they've told me it must be my WiFi and to contact Sky. All of the household phone settings are exactly the same and no VPNs

[JimM1]

@Juniper275 If you have one problem device connecting, and all others are fine, then what have you done to look at this event? You do not even explain what is going on, Apple say's its nothing to do with them, so what speed were you getting when they tested it at the Apple store if that is where you went?

[Juniper275]

All devices connect at 110mbps, my phone is 20mbps or less. I have done all of the troubleshooting through Apple and all of the Sky troubleshooting. It connects to WiFi outside the house, including the Apple Store. No hardware issues are shown on my phone and a full factory reset has made no difference. I'm just not sure why it's just this one device in the house