Workout results have both a SCORE and DETAILS. The score (time, total weight, heaviest load, total reps etc) shows up on the whiteboard and is used for ranking, and workout performance trend. The details are what drive most of the valuable reports in WODTogether.
When you log a workout result, the details are optional. It usually only takes a few extra seconds to fill them out, and often times they are at least partially filled out automatically. Details provide the data for complete movement history, including benchmarks.
If your benchmarks aren't updating, check your workout results to make sure you included the weights/times etc in the Result Details section.
The other possibility is that you logged against a movement that the system does not show on the benchmark screen. For instance, if you log a "pause snatch" it will not update your "snatch" benchmark.