It is the first time in my life that I hear that. I know that sometimes winrar can open corrupt files (it seems winrar can fix errors or at least ignore and unzip) while 7zip needs the file to be uncorrupted. but the problem is a corrupt file and if that happens to you in itch, it is better to discuss it with the developer.
EDIT
PS: I don't doubt what you're saying, what I'm saying is that if 7-zip can't open a .rar, it's probably a problem with the file and instead of looking for ways to bypass the problem (there are programs that can fix errors like a bad CRC) it's better to inform the developer.