The cause of the disappearing shadows is essentially a limitation and the solution is to make changes to the game as described in the player log:

"Too many additional punctual lights shadows to look good, URP removed 22 shadow maps to make the others fit in the shadow atlas. To avoid this, increase shadow atlas size, remove some shadowed lights, replace soft shadows by hard shadows ; or replace point lights by spot lights There are too many shadowed additional punctual lights active at the same time, URP will not render all the shadows. To ensure all shadows are rendered, reduce the number of shadowed additional lights in the scene ; make sure they are not active at the same time ; or replace point lights by spot lights (spot lights use less shadow maps than point lights)."