We've got over 20 years of experience with cigars and every time someone tells us they're having issues with humidity we always check these 5 things...
And the most important thing your humidor must have is a good seal. When your humidor is open there should be an obvious lip that seals in humidity when the lid is closed.
Many people will tell you to wipe the inside of your humidor with distilled water. Do not do this! This can cause the cedar to warp and, even worse, crack.
The most common type, the dense green foam, holds liquid (often distilled water or special humidifier solution) and releases it as moisture in to the air.
However over time these humidifiers become clogged and damaged.
These humidifiers should hold about 1:2 their volume in liquid - if yours isn't holding that much it may be clogged and need replacing.
Eventually we thought to check the location of his humidor and realised it was just around the corner from his shower. Every time someone had a hot shower the condensation would play havoc with his humidor.
So check to make sure your humidor isn't sitting somewhere with outside interference.
Pro-tip: Too much direct sunlight or heat will mess with the levels in your humidor.
Analog hygrometers use a spring which is "tuned" to a certain humidity and that spring can wear out over time. So if it's showing 50%/60% it may be misreading the humidity.
If your cigars feel fine then they probably are. And if you're still worried grab a digital hygrometer. Even a cheap digital hygrometer will give you a much more accurate reading than an analog one.