On 10/29/20 14:37, Mike Hammett wrote:

Have you ruled out local wireless issues, such as a literal side-by-side test?

Yes - all other wi-fi devices don't exhibit this issue, including my wireless-connected PC. Only this MacBook running Catalina.

The problem exists at all wi-fi AP's around the house, all of which are easily 15m apart to cover the whole house.

Does the problem still exist when wired?

No problem on wire. As you can see below, my worst record latency value is 11.8ms only:

Marks-MacBook-Pro.local (172.16.0.239)                                                                                                                                                                                         2020-10-29T14:48:12+0200
Keys: Help   Display mode   Restart statistics   Order of fields   quit
                                                                                                                                                                                                               Packets               Pings
Host                                                                                                                                                                                                        Loss%   Snt   Last   Avg Best Wrst StDev
1. 172.16.0.254                                                                                                                                                                                              0.0%    50    1.0   2.6   0.7 11.8   2.1

Mark.