Task disappeared in Prop Challenge mode

When I create a Prop Challenge mode and then close the project, when I open the project again later, I notice that the Task part in the project often disappears and can't be retrieved. This means I have to keep creating new projects all the time and can't save it and continue working until the project is completed as intended. Sometimes it still shows up when opening the project for the second or third time, but eventually, it disappears anyway, even though the conditions I set are positive and haven't been violated.