3rd Site-to-Site VPN added, stopped traffic on the other 2 S2S VPNs

Question

I have a single VPC and sing VGW.
I have two active S2S VPNs, each going to different subnets on the client side. They both connect to "subnet a" in AWS. This works fine.
I tried to add a 3rd S2S VPN, that tunnels one IP address on a new client and one IP address in the same "subnet a" in AWS.
As soon as this 3rd VPN comes up, the other 2 VPNs stop passing traffic.

I suspect that this is a routing issue. Though I would have expected typical routing behavior to prevail: Where if the most specific route doesnt apply, it moves on to the next. I must be missing something simple here!
Thanks in advance for any guidance.

Edit: All three are static route based VPNS

Answer

You shouldnt have overlapping static routes with multiple VPN tunnels terminating on same VGW.

You will see weird behaviors like this and the AWS VPN tunnel selecting logic for Egressing out of VPC cannot be controlled in such scenarios
This might be expected with the overlapping static routes you have in place.

Is there a reason why you have Overlapping network routes routed via Different Tunnels in the first place ?
Maybe it will help if you can clearly specify the routes added via Each of the Three VPNs.
VPN-A: Static route ?
VPN-B: Static route ?
VPN-C: Static route ?

3rd Site-to-Site VPN added, stopped traffic on the other 2 S2S VPNs

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