"PL/SQL lock timer" wait event is not written into ASH (v$active_session_history/dba_hist_active_sess_history)

Recently I investigated some database lock issue by digging into ASH data. I accidentally found that while session is in 'ACTIVE' state and 'WAITING' on "PL/SQL lock timer", no rows is added into ASH.
So if you trying to figure out what was happened in the past, you can find that some active session disappeared from ASH for period of time. And only manually made snapshots of v$session can give some real info.