I'm skeptical that this one minute jitter period is solely attributable to one minute timers in power inverter equipment. It's likely the net scale effect of all cron-like scheduling of actions in everything with a microprocessor. All the long-term scheduling that is done with minute precision (i.e. seconds field is implicitly :00) regardless of its individual period. Like if one device is scheduling at x:17 and x:47 every hour, another one is doing x:06, x:09, x:12, x:15, ... and numerous other combinations, at scale, the common divisor will be one minute. If wall clock time is used, all the devices that are synchronized to a network time will have cron-like scheduling events firing at xx:xx:00 for all values of x.

This type of scheduling should be randomized at the seconds level, perhaps. Unfortunately, it would require a massively coordinated effort across numerous operating system and application stacks.