[Pitfall] How to recover the disappearing vertical lines of multicolumn/multirow cells in Latex

Disappearance:

Fix:

1. The first point is to ensure that the number of cells is correct ;

2. The second point is a small detail. You need to add a "|" after the c here :

\multicolumn{3}{c|}

        Of course, if the left side is less, then add the left side; or it is easiest to just add both the left and right sides:

\multicolumn{3}{|c|}

Repair effect: