I recently upgraded to mercurial 3.0 and to hgsubversion tag 1.6.1 and I am seeing corruption in the files I have cloned.
After reading a similar issue I ran clone with the --stupid option and was flooded with Hunk Failed messages. After letting it run for a while it crashed with the following message:
"svn: In file '......\subversion\libsvn_ra\ra_loader.c' line 595: assertion failed (*path != '/')
This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information."
Unfortunately it is a large internal repo and creating a smaller sample would be difficult.