Reference Material:

https://aws.amazon.com/premiumsupport/knowledge-center/troubleshoot-bgp-dx/#:~:text=If%20you%20are%20advertising%20more,go%20into%20an%20idle%20state.&text=If%20you%20have%20more%20than,the%20BGP%20session%20to%20AWS.
Check the BGP session if it changes from established to idle state
For private Direct Connect VIFs, verify the number of routes that you are advertising over the BGP session. If you are advertising more than 100 routes over the BGP session, the BGP session will go into an idle state. Summarize the routes so the number of advertised routes is less than 100, or advertise a default route over the BGP session to AWS.
If you have more than 100 networks in your on-premises network, you can advertise a default route over the BGP session to AWS.
You can summarize the routes so that the number of advertised routes is less than 100.