1. First of all, the first case may be caused by the disconnection between the engineering drawing and the parts. Just re-establish the connection, as shown below, and then go to the next step.
2. As shown in the figure, open the engineering drawing with software, and the opened interface has a reference item. Click Enter, double-click the file name, find the part to be connected again and confirm.
3. Then, after completing the above steps, in the second case, a view disappears. This may be caused by hidden drawings. Click the corresponding view, as shown in the figure below, and then enter the next step.
4. Finally, find the missing drawings in the design tree on the left, right-click to find "Display", and then click "Display" to restore the hidden drawings, as shown in the following figure. In this way, the problem is solved.