It appears you are encountering a bug with Jive cloud at the moment CLOUD-522:
CLOUD-522 -Recent Video Widget: Does not show video thumbnails
The bug is currently open, therefore I do not have an ETA on the resolution. However, if you would like to be notified when our Engineers have resolved the bug, feel free to create a case in your Private Support group and provide the Bug ID. Our Support team will then update the case for tracking and notify you when the bug is resolved.
Hope this helps.
Thanks for this information. I'll create a case in our Support group.