Storyline course wont launch in MS Edge

1. When you publish, do you make sure to delete previous output folders?
2. What is the target file you are using to launch?
3. Do you make sure that Storyline is up to date before publishing?*

All three can cause issues.

If you overwrite an existing folder when publishing, legacy files can be retained, which can cause a variety of issues. Makin sure it's a clean publish each time can avoid issues.  

We have had issues with content where Developers were overwriting content, and hadn't been updating Storyline 3. So we had some persistent issues when Flash passed End of Life, and when Synchronous XHR was deprecated.

And where some courses were set up to use poor target file (not index_lms.html). Older versions of Storyline had more target file options, and some would roll over to the one best for a browser, and others couldn't (and cause other functional issues on the LMS).

It could also be something with your organizations browser settings. I would consult with your LMS admin and back end support, as well as your IT team responsible for browers. The lengths your IT team may have had to go to in order to keep legacy systems working prior to IE11 End of Life were likely Herculean, and I'm sure there are still some holdovers from that.  It may be that your browser settings go quickly to Internet Explorer mode because of that. 

Recommend checking all the above, and using debugging mode to isolate the cause.

*We use Storyline 3, but I assume Storyline 360 operates with a desktop client which could get out of date.