For Dropbox, I don't understand why it happens. I always test the download link prior to posting it, and I download it on another computer after that, and it works fine. But if someone else has any idea, I'll be glad to test it.
To help folks on Discord, I had to download your mod, unpack it, then pack it into .zip archive, afterwards there was no problems with unpacking, mod worked properly.
If someone doesn't have WinRar or similar program which recognizes .rar files, they will have problem with unpacking your mod.
Windows recognizes .zip files without any other software, so saving your mod in .zip archive will be better for end user.
Problem with people not being able to unpack your mod may have to do archive format you're saving the mod in.
Maybe because you're using RAR5 format instead of RAR?
I did test it out, downloaded your mod.
Made 3 archives which I sent to another user to test if it worked for them.
.zip - unpacked properly
.rar (saved with RAR format) - unpacked properly
.rar (saved with RAR5 format) - error when unpacking
Person in question was using 7zip.