@Tommat,

It is likely because you are trying to get more than one router running on a network, which is not recommended without some very advanced configuration.

The easiest method since you are keeping the Starlink Router at the head of your network would be to just setup both of the Archers as Access Points - this will leave your starlink router in charge of things like routing and the DHCP server, while your Archers while in AP Mode will be in charge of providing the wireless network from your home. 

If you can, you can disable the wireless network on your starlink router, or configure your Archers to use the same wireless credentials so that devices can connect to either.