This has already been reported to the developers based on another thread: https://discussions.scouting.org/t/bug-i-am-unable-to-add-hours-service-camping-etc-after-completion-of-an-event/439121/4
Your best bet to find out when it has been resolved is to watch or subscribe to the change logs for Scoutbook Plus here: https://discussions.scouting.org/c/scoutbook/scoutbook-change-log/
