Please have a look at the following Research Gate threads,

https://www.researchgate.net/post/What-are-all-possible-reasons-for-the-peak-shift-in-X-Ray-Diffraction#:~:text=The%20peak%20shift%20in%20XRD,shrinking%20of%20the%20XRD%20peaks.

https://www.researchgate.net/post/What-is-the-reason-of-peak-shifting-in-XRD-towards-lower-or-higher-angle-after-the-polymer-sample-has-been-heat-treated

Safdar Ali, what is the crystal structure of your samples?

Chian Heng Lee, Hexagonal