It’s not technically an issue because it IS installing. Unfortunately we’ve all been fed a lie by Microsoft since the early 90’s: Loading bars are extremely inaccurate time-wise.
Around 82-83% it has several large files to deal with, and the graph is only updated based on # of files finished, not actual data speed. It’s extracting space filled/time but only updates on completion so it gives the illusion that it’s doing nothing… Don’t worry, it is. And it’s not Epic- it’s just the nature of progress bars. I’m sure if they could break that file down for easier downloading in pieces they would.