Both computers are connected the same Unifi network. One was a Macbook Pro using the builtin wireless (ac; listed as 144 Mbps in the Unifi controller iirc) and

Both computers are connected the same Unifi network. One was a Macbook Pro using the builtin wireless (ac; listed as 144 Mbps in the Unifi controller iirc) and the other a Mac Mini connected via cable (1Gbps). They both pinged the router, so all traffic was local. There are no other wifi networks nearby (single family house area, 50+ meters between houses), and basically no other traffic on the network.