Have you tried to just embed that link in EPIC directly without going through tableau? i would try that first and see what behavior you experience before routing through tableau. Seems to me it may be a challenge with EPIC, and not Tableau. what browser version are you using?
There are too many layers here to exactly pin point where the problem may be. It could be your browser, it could be how EPIC interacts with the browser, it could be a protocol issue between EPIC and sharepoint, etc.
FYI, the browser in Epic is a version of IE but not a full IE client. It's at least a few versions behind. Prior to our Epic upgrade to 2015 it was still only IE 9 (I believe).
What happens if you copy that link and directly paste it into a browser (any browser) ?
As I stated earlier, this doesnt look like a tableau issue, or one that tableau would have control over.