It shouldn't be happening on a new script placer map. // That error comes from using a command like flag_wait "all_players_connected" before flag_init "all_players_connected" If you have developer 1, developer_script 1, and logfile it should tell you the exact file and line the flag is called from.
Map_source contains prefabs and maps. Mods/mapname/ contains custom scripts sounds ect. Zone_source contains csv associated with your mapname. Custom models and textures will need the gdt and original files associated with them. // Create a new map with a script placer on your new computer. Compile and test it to be sure you installed modtools and updates correctly. Replace your NEWmapname.map with your OLDmapname.map Copy any csv edits into your new map csv. Copy any custom scripts over and update your mapname.gsc
Look in the console when it freezes for anything important. Check your mapname.gsc and see if you added anything twice by mistake. If it happens when you get items and when the game starts maybe your player quotes are not setup correctly.
Water sometimes cuts horizontally though the map when its compiled but its supposed to fill the brush volume with water. I dont think there is a perfect solution but i would try one of these. Make sure it has structural brushes around it to define the boundaries. Try using a no_draw_decal brush with water texture on one face. Terrain patch. Curve patch. If none of those suggestions work i have a dynamic water texture and a scrolling foamy texture/model i used for a waterfall and stream i might be able to upload.