I agree that those speed tests look totally normal (good, in fact) but the opening message was complaining about web pages not loading or timing out.
As one can now rule out internet speed/bandwidth as an issue I wonder if it’s a DNS resolution issue? I used to get those and my solution was to go into the admin pages of the Horizon box and change the DNS servers to google’s (188.8.131.52, 184.108.40.206). I’d suggest trying that. However, I’ve not had that for a while now and I reset the DNS servers back to the default (by putting 0.0.0.0 in the DNS fields).