This was driving me crazy for a week. Some jobs were showing the trends graph, others were not.
Eventually, i solved the problem; your job's name must begin with a lower case if you there are any other upper case characters in the first word. Confused? Here's an example;
OvernightBuild_Test (graph will not appear)
overnightBuild_Test (graph will appear)
Overnight_Build_Test (graph will appear)
If you rename, it will appear (including all previous builds)
