Why does my Linksys MX4200 slow down with HomeKit?

I run HomeKit in home with typically 20 devices in service on 2 meshed Linksys 4200 routers. devices split about equally between 2 & 5 Ghz bands. I have found speeds for apps (streaming, web access, etc.) degrade as the week goes until I have to restart the router to get back to useful service. But when I test raw ping speed if is fine (~ 450 Mbps down & 10 Mbps Up).

Anyone else have this issue? Suggestions on what to do? (Note, these routers are still one of the recommended models for HomeKit in several of the rags).

[Re-Titled by Moderator]

Original Title: Linksys MX4200 Performance with HomeKit