First you're going to need to spill the beans on what mfg they are, we're all professionals here wanting to learn more and who to use and who to stay away from.
There are all kinds of reasons as to why.
I'm going to gamble and say their chinese, their constant voltage not constant current.
When you use constant voltage then what is the voltage output on the line in operation? Less than 12v, 12.25? The slightest fraction of a volt above 12v can kill a system very fast. Which is a big reason why a lot of these LED mfg's say their products are only warrantied with brand X power supply, etc etc. Are you using a 60w PS?
With regulated CC LED's where they are regulated, that +/- voltage won't damage the modules.
We've been testing every LED mfg since 2008 and I would only use 5% of the LEDs we've been testing because frankly majority are Chinese, their CV and light degradation is awful. Very few put out enough light compared to conventional light sources, a nice bin, and last at least 15,000 hours with only 3% lumen maintenance, in fact contrary to their brochure marketing statements a lot are about 30% at 12k hours of operations, and of course a lot will depend on the wattage of the module. The higher the wattage, the brighter the module the more heat they generate, and we all know a chips worst nightmare is heat. It all boils down to a trade off, More light, less life, less light more life, and there are of course other factors involved that pro long life, but I've never seen a chinese LED module that's impressed me.
Stay away from "Engineered in America, Made in China".....unless of course your the type of shop that likes to just collect a check and take off, but I don't believe there are that many that make that their business standards, that's my 2 cents