Hey

Yes, once you complete the instance regardless of the star completion. You'll obtain the fragments.
Obtaining all the stars gives you the coupon reward not double the fragments.

Maybe you were mistaken?

Judging from your level, You've completed Chapter 8 quite some time ago.

Unfortunately, due to the time range, it'll be hard to determine if you received them or not.
However, Feel free to post it here

Follow the threads instructions and we'll get to you shortly.