I am also using the updated excel export code, and it works great for a smaller dataset but with a larger set 14K cells it gets stuck.
If I disable the section of code that adds borders it works fine and still produces a good result
cellSelection.SetBorders(New CellBorders(leftBorder, topBorder, rightBorder, bottomBorder, insideBorder, insideBorder, Nothing, Nothing))
Not sure why, changing underlying collection and getting stuck in a loop? or if the cumulative effect of this size dataset is too much and it starts to slow?
I'm afraid I'm a little pushed for time to explore this further, but thought it might help if anyone was having the same problem