OK, I am surprised this haven't come up earlier. I am also not aware of any major software upgrades that could have influenced this behavior.
Anyways, I think I pinpointed it down to our proxy server which didn't properly forward all svn requests to the underlying Apache server. Until we solved the problem, could you try accessing the Apache server directly via:
https://dev.mobileread.com:8080/svn/[yourproject] (so same url as before, but on different port)
Best,
Alex