Yup, try opening the vSAN Observer bundle from a computer with internet access. The graphs.html and stats.html have some references to scripts e.g. to https://code.jquery.com (you'll find this running e.g. Chrome in "Developer Mode", and look for what's "stuck on loading", e.g. "connecting to netdns.bootstrapcdn.com"). If you have internet access, maybe some of the are blocked? (you'll find out when running in "devmode"). If I remember correctly, boostrap.min.js also have some additional references (you'll see this when accessing the "Disks Deep-Dive view").
If you don't have internet access, you may also download the scripts, and do some quick & dirty "hacks" on the vSAN Observer pages (e.g. directly in the graphs.html and stats.html), putting the necessery files somewhere available - them the pages will load just fine. Both works when files available (e.g. vSAN Observer directly from vCSA and/or exported bundle). Would be nice if files where included directly in vSAN Observer-bundle, but hey; guessing this just is a tool for VMware / technical geeks now days .
These machines definitely have internet access, will try dev mode.