What is causing a white scale buildup at copper pin connection on LED light sticks and how can they be cleaned?
Copper is a material that corrodes, just like any other. When copper corrodes, it will turn into copper carbonate (Cu2CO3(OH)2), but near the sea it might become copper chloride (Cu2(OH)3Cl) as well. When water is involved, like in your case, there may be an effect called efflorescence. Efflorescence "is the migration of a salt to the surface of a porous material, where it forms a coating". This usually forms in a crystal form, since it's formed of salt. This is what creates the white buildup sometimes found on water pipes for example:


https://diy.stackexchange.com/questions/86004/green-and-white-stuff-on-copper-pipes

In your case it's the same:


So basically, you're getting water infiltration. The easiest solution to solve this is using dielectric grease. Or get a better seal for your electronics.