I have a zimbra server running at more than one year and who also does some days we are having the same problem (failed to load yahoo! Maps API), besides this problem I have a growing log in /opt/zimbra/zmstat/zmstat.out that came to bringing 11Gb performance problems and even paralysis of service.
I spotted a bug logged for this case zmstat.out - https://bugzilla.zimbra.com/show_bug.cgi?Id=42332
From what I've seen in the documentation seems to be a problem with JAVA, API, and unfortunately I could not identify the cause, but I'm working on.
If any have any further information that might help please post here.