Sometimes, if I close and open CGminer, it drops from customary ~330 on intensity 13 to less than 20. Additionally, the computer starts lagging as much as it does on intensity 16+ during normal work (when it's set at 13, it is normally usable with no lag at all). Also, GPU isn't 100% loaded, as is typical (though GPU_MAX_ALLOC_PERCENT is set to 100). Restarting CGminer or modifying settings doesn't help (I've tried a lot). This happens on all pools. Driver version is 13.12. GPU is the Sapphire Vapor-X one. I tried SGminer, but it has the same problem. Restarting the computer fixes the issue, but that's not really a solution.

What could be causing this?