Summary

VM configuration in VHI has 2 network interfaces with default Gateways. After VM creation it has 2 default GWs and as result not working network (in this example VM OS: Ubuntu 20.4). Ping is not possible and, packages sent to one GW replied to the other one. 'ip a' shows 2 gateways configured.
 

Resolution

Use custom cloud-init configuration on the VM creation stage  for removing second GW:

insert following script:

#cloud-config
bootcmd:
 - ip route del default via 10.10.2.1

where  10.10.2.1 - is GW IP that should be removed. please replace it with correct one.
Insert the script code into text field, or save it into some file and load on to that page.