Sorting buttons are in incorrect location depending on window size.
Examples:
Good - Both buttons in correct location.

Bad - Bottom button is in the wrong location.

My normal resolution for playing mc - Both button are in wrong location.

Thank you for the detailed report, does this take care of the issue?
InventorySorter-1.5.1.jar.zip

It's better, but its still oddly placed:

I edited the comment right as you downloaded, can you redownload?

Yes it's fixed now:

Fixed in 1.5.1, released on curseforge