Hello @wakecarter
I’m not sure what exactly worked, but I deleted the online files as you suggested here "Unknown Resource" online, but works fine offline? - #10 by wakecarter and recreated the online project files after adding the videos in the Additional Resources section in the Online tab of the Experiment Settings. I also used Ctrl-Shift-R in the Project Dashboard.
Thanks a lot for your help! I greatly appreciate it 
Best wishes