The Weather Underground is an awesome resource for watching real-time data around the country from personal weather stations. Weewx can publish data to the Weather Underground as an option.
However, occasionally data doesn't make it on to WU. The problem seems to be flaky servers on their end. There are ample discussions on the WU forum on wxforum.net about the problem (see this thread, or this thread for two of many such examples).
I wrote a utility in Python to look for these missing data. You give it a day (e.g., "2008-06-22"), and it then compares records in the SQLITE archive against what has appeared on the corresponding station on WU ("KORHOODR3" in my case), noting any missing data. It can then optionally republish them.
Because wview (which I used before writing weewx) uses an identical schema, this utility can also be used by wview users.
Wunderfixer has been included with weewx since release 3.2.0.
See the wunderfixer section in the weewx utilities guide for instructions.