Several users use Streamable.com to show short videos on this forum (mainly demos). Often all I see is the embedded player OK, but instead of a preview, I get a white blank screen and the video doesn’t play. Other users have reported this too. (Oddly, for some forum members there are no problems).
Steve mentioned that it could be due to expiration date of the video:
I found that if I paste the link to a “Streamable” video directly, THEN select the Hyperlink icon in the “Create a new topic” pane on this forum, and copy the link again, when the post is submitted, the video works as expected, both on the embedded player and also if I click the direct link text.