Should you have adquired tasks in your BPM instances that the user didn’t released beacuse abrupt window closing or software implementaion issues/faillures maybe you are querying the BPM engine only for tasks asigned to the group or yourself (me and my group).
BPM has a default configuration of 3 days for task AutoRelease that you can change (see official documentation or https://blogs.oracle.com/soacommunity/entry/how_to_configure_oracle_soa
Anyway, a good idea is making “world class” software by giving end user as much information as possible in order to help resolve issues in a more intuitive way. In this particular case you could query the BPM engine not only for assigned tasks but others such as adquired by others, failled, etc. Is the way the standard worklist app does.