I have devices that use Xilinx XC9572XL CPLDs. They haven't been used (as in: not powered at all) for almost seven years, and symptoms would point to the CPLDs being at fault.
I couldn't find much on the durability of non-volatile storage in CPLDs. Is it possible that storage has deteriorated enough over 7 years to cause problems?
More generally, how long is a CPLD expected to last once programmed?