ZM 1.30.4, Ubuntu Server 14.04 LTS (204 days uptime

Event storage to FreeNAS via NFS. Accessed over very slow DSL.
I'm doing a continuous record on a PTZ camera on "patrol". (1920x1080x10fps)
When I go to export a given 10min event (event details, frame details, image files) the export popup just does the travelling export thing (Exporting.......) but export never completes and nothing downloads.
It's working as expected on a local ZM server (zm 1.30.4, Ubuntu Server 16.04.3 LTS, local storage.
There are a number of things that could be causing it to fail/not complete; storage differences, local net vs vpn over dsl, version of server OS.
So I thought I'd ask the guru's if there was a command line or series of steps I could do on the console of the ZM server to step through and export and see what's going on.
BTW, I don't want video, I prefer the individual frames for forensic use; good on you all for making video record optional; it has it's place, but you can't beat the individual frames for clarity!
Thanks