I have a very similar issue that is very difficult to diagnose purely down to the Appliance not having what I deem useful diag tools 

Also struggled to find any logs files as they all seem to be geared to looking at something that has previously worked

That said I have recently found that you can obtain trace route and telnet from the repo

If your appliance has outbound internet you can do this online

https://vmware.github.io/photon/assets/files/html/3.0/photon_troubleshoot/installing-tools.html

If your applianace is not online (like mine) you can obtain the rpm packages and manually copy to the /tmp directory and install

https://kb.vmware.com/s/article/88553

Repo is here : 

https://packages.vmware.com/photon/3.0/photon_release_3.0_x86_64/x86_64/