In the after commit, do you change the object itself? In that case you have to commit the object again (without events, to avoid a infinite loop). If you change the object without commiting it, the attribute is only stored in memory but never sent to the database.
In this case you might want to use a before commit microflow if possible, so you don't have to use two commits.
If you change another object, make sure you commit this change as well.
Hope this helps!