Ethernet cable seems to switch off the Wifi connection

[Windy78]

Hi, advice please.....we have a Hub 4 and also use Eero boxes to boost the Wifi connections around the house.  All seems  fine technically  with this set up which we've used for some time.  The base Eero unit is connected into the Hub 4 in port 4.

...but one of our household is a gamer and lives in the furthest away room from the Hub.  He has been connecting through the Eero wifi.  This gives a connection speed of just over 100mb but with a variable ping rate which is fine for 'normal' use but does create lagging when gaming. 

When we plugged the gaming PC via a (long) cat 6 Ethernet cable into the Hub 4 (into port 1)  it gave the gaming PC a 1gb internet spped and consistently good ping rates, which was great for gaming.....

.....however when we plugged in the ehternet cable this seemed to cause the Eero connection and therefore the Wife to stopp connecting to the internet via the Hub.   We've tried rebooting the Hub and the Eero box, but get the same thing, i.e. when we plug in the ethernet cable the Eero drops its internet connection.  

Can anyone advise what we need to do to enable both the ethernet connection to the gaming PC and the Eero to connect to the virgin Hub at the same time?   Thanks.  

[Adduxi · Accepted solution]

If the Hub is in modem mode with the Eero doing the Router work, then you can only use a single port on the Hub and it must be connected to the Eero.  If you need more ports, just buy a simple unmanaged gigabit ethernet switch and connect it to one of the Eero's.  Do not put the switch between the Hub and the Eero however !

[Windy78]

Thanks.....we had the 360 mini box wired to the eero by ethernet, so we reset the mini box to work by Wifi.   Then we plugged the gaming PC straight into the unused port on the Eero box.......works like a dream.    
Thanks for the insight about not plugging the ethernet cable straight into the hub when it is set in modem mode.  Really useful.   

[Adduxi]

Yes when in modem mode the Hub is just a “bridge” to the VM CMTS. Simplified the CMTS will allow only one device access, so if you have two cables in it’s anyone’s guess which will get access. Hence the restriction to one connection.