ISP:  Spectrum 300 Mbps (typically I am getting 600 Mbps measured with fast.com)

Modem:  Spectrum Hitron E31N2V1

Router: (3) Deco X20 AX1800 - Firmware is up to date.

2 Win 10 PC's connected to Deco X20 via ethernet cable.

1 iMac connected to Deco X20 via ethernet cable but this one is usually off.

For 2 months I was consistently getting 300 - 600 Mbps on each computer.

For the last 3 days I have had 3 random speed drops to below 100 Mbps.

Rebooting the primary Deco X20 brings speeds back up to 300-600 Mbps.

Today I just rebooted the Spectrum Modem and speeds returned to 300-600 Mbps, but I  think rebooting the modem caused the Deco X20 to reboot also?  Not sure?

Since each computer is connected via ethernet this is not a wifi issue, although when there is a speed loss on ethernet there is also a corresponding speed loss on wifi.

This is getting annoying, something changed over the last few days.