I recently got a set of three M9 Plus routers that are now setup in my house: fiber box <cable> main M9 <cable> secondary M9 <wifi> third M9.
The secondary M9 is where most of the traffic goes, since it is in my living room (2nd floor). Primary M9 is on the first floor and third is in 2nd floor hallway, about 10 m away from the second.
Measuring wireless bandwidth gives me good readings in all places and a low ping value, but if I set up a long-running ping I see recurring long delays every 30-90 seconds or so. Typically it goes from <10 ms to >500 ms for a few seconds, then back again.
When connecting by wire to the second M9 these glitches go away.
This doesn't really affect most of my day-to-day use like music streaming, surfing or watching Netflix or HBO, but it has a huge impact when using video or audio calls (Teams, Slack, Hangouts etc). Performing calls with wired access takes away pretty much all glitches, so it does not seem to be related to my ISP.
I have something like 25 different devices connected, cameras, printer, game consoles, stereo and I'm normally using Apple devices (MacBook Pro, iPad or iPhones) to browse and work.
My house is reasonably far away from surrounding neighbours (>50m to the closest neighbors, four in all) so radio interference from them should be minimal, although I can detect their networks. most of the time.
Any advice appreciated!