Running WU RF with a station such as an Acurite (that provides partial loop packets) can result in some unusual results. When RF is enabled WeeWX will report whatever it can from the data available in the loop packets received from your station. You could try running WeeWX directly (http://weewx.com/docs/usersguide.htm#Running_directly), this will show you the loop packets (lines starting with LOOP:) and archive records (lines starting with REC:). WeeWX can only report what is in those packets/records. So if field rain only appears every so many minutes or every archive record then that is as often as it can be reported.
Gary
$ sudo weewxd /etc/weewx/weewx.conf
Gary
It is quite possible that WeeWX is posting the data but WU is somehow ignoring/losing/butchering it.
Gary
Suggest you set debug=2 if not already done, restart WeeWX and post a log extract covering a good 2 to 3 archive intervals. A sanitised copy of weewx.conf would help too. You can use wee_debug for this just check the output before posting.
Gary