I cannot see seminar lessons in class's timetable

This situation happens when there is no student from this class assigned for given seminar. In such case a card "without class" is created and can be placed only into teacher's timetable.

The solution of this situation is either to sign some student from this class to this seminar or erase this lesson from teacher's contract.

Note: Similar situation can happen also for seminars where there are joint students from two classes. In such case it may happen that there are students only from one class signed for this seminar and so the card is shown only on this class's timetable. If you wish this card to be shown also in other class's timetable then you need to sign some students from this class to that seminar.