The initial click event from the UI is asynch. That thread starts a search activity. Upon the activity completed event, another activity is started (this activity contains the click shown in the logging) using an asynch thread as well.
I re-interrogated the control element that was causing the issue. I was originally matching the <span> element, but re-matched to the <attribute> element. The error was very frequent (multiple times per day), but has no longer occurred after this change was made (few days of successful testing).