We have a server with both a /31 and a /24 in different /8s statically routed to it. We have a gateway in the same /24 as the /31.
Incoming connections to IPs in the /24 work as expected, but we are unable to initiate outgoing connections. Our "gold-standard" test is (using an IP to avoid dns issues at this point):
curl --interface SOME_IP_IN_THE_24 -v -H 'Host: httpbin.org' 34.230.136.58/ip
We're using Ubuntu 16.04, and we've configured eno1 with one of the /31, eno1:1 with the other /31, and eno1:2 with one of the IPs from the /24. When we run the command above, we still get the IP for eno1.