That probably referred to "PID", Potential Induced Degradation, where ions driven into the cells affected them.
Some cells are P-type silicon with N doped layer, others are N-type with P doped (I can't remember which is conventional and which SunPower uses). SunPower cells were supposed to be of a type that lasted longer in the sun, but when configured with negative terminal grounded the more positive biased panels degraded.
SunPower fixed that with material changes (glass and epoxy), and the data sheet for the panels above says, "PID Test 1500 V: IEC 62804". Some other brands still suffer from PID. Most grid-tie inverters today are transformerless, with PV string floating half biased above ground and half biased below, so subject to PID if not resistant.
I have smaller 327w panels of the E20 series. Fine so far, but of course I don't have long-term data.