A stacking program much used by astrophotographists is autostakkert. It's free and works very well. Maybe worth trying. https://www.autostakkert.com/
Unfortunately, the meaning of the term 'stacking' differs between Astro and Micro work.
In photomicrography, it involves stacking focus [Z-axis] layers to improve the depth-of-field.
In AstroPhotography, it is mostly about alignment in X and Y axes, and noise reduction.
Edit: Here is an good introductionhttp://zerenesystems.com/cms/stacker