When trying to open a video I always get this message 'Adobe Flash Player not allowed". If I right click I get a message saying "allow this plug in". I click that and the video works. Sometimes the right click does nothing, so I cannot view the video.
I'm concerned about the "allow this plugin" menu item that you describe seeing sometimes. This doesn't sound like a default Chrome menu. Could you try temporarily disabling all of these to see if one of these is blocking Flash and is the owner of this menu item?