map_pack.bsp cache sometimes stops updating on servers

In #next-update, Redox reported servers where cache/map_pack.bsp stops updating, so new maps load lumps from previous ones until a restart. Rubat said it must be written to disk and may need more error handling, and listed the related log messages. They have to be searched for in console.log with -condebug, which Redox avoids for performance; Cynthia suggested enginespew.