Same issue as well...embedded to a sharepoint site. I really hope there's a workaround for this.
Same issue noticed as well. Images embedded via Web page container work fine in the desktop app, but fail to load online unless you switch to https.
I am experiencing the same issue. This broke our quarterly reporting dashboards. Has anyone figured out a workaround? Is there any response from Tableau Support? 10.3 didn't address it as far as I can see.