This looks like the same issue as the PDF thumbnails sometimes not displaying. This issue is being looked at by the PLM 360 Development team and I will let you know when I have more information.
Thank you for pointing this out.
The DWF thumbnail is working for me using IE9. I'm still testing as to why it is not working in Firefox.
I'll let you know when I have more information to share.
Thanks for the reply. It works for me also in IE9. However for me (and a lot of other people here) IE9 crashes continuously so we use Firefox. Keep me posted with your findings.
I've escalated this to the PLM 360 Development team and they are aware of this issue and are evaluating the symptoms.