thats the beauty of decompliing a .BSP things get broken, when you load up your decompilied vmf you migt be lucky and get a warning of brocken brushes if you do’t it doesn’t mean there are none, you need to go over the map and check brushes are ok, thicker than 1 unit and are on grid, the best tihng to do before you edit a decompilied map is to check it compiles ok to start with
1st do alt +p to display any errors if any are shown fix them, then do a compile just the vbsp that will sow up any leaks fix them, then in the 2d view after setting a grid size of 4 scan over the brushes and check there on grid and not 1 unit thick once thats done save and do a full compile
if you have loaded the pointfile follow the red line to the outside void and close the gap between the brushes if theres no gap check that the wall it goes throu isn’t an entity if it is change the entity back to a brush
Is it going upwards? if it goes straight up at an angle then it’s an areaportal leak. If it’s zigzagging around other walls and going through a specific wall, that wall is either a func_detail, which should be moved to world, or has a translucent texture on it, which should be replaced with an opaque texture.
Sometimes certain maps like to replace nodraw with playerclip, which is hell to fix and you should just give up. If it had compile protection, one of the things it does is not fixup cubemap faces (not too big of a deal to fix, but can be annoying. Won’t stop a compile though.)