It could be any of the things that you mentioned. You don't need to re-season after doing the flashlight test, the point of seasoning is to get water into the wood, so that it isn't soaking up more moisture from your cigars. Once you have it seasoned, you shouldn't have to do it again unless you leave it totally dry for a while (like weeks). If your humi is well seasoned and you don't have any correctable leaks, adding a water pillow or getting more beads isn't a bad idea. You will always lose some moisture through small leaks and even through the wood itself. If the amount of beads you have isn't able to release enough moisture quickly enough, you need to find another way to provide moisture.
I've actually started recharging my beads using a water pillow. When my humidity starts to drop, I just soak a pillow with distilled water and toss it in the humi.