ReadyNAS 516 strange SMART Load Cycle Count on SEAGATE disks, not on Western Digital disks

I have been operating this ReadyNAS 516 in the home environment for the last 8 years. Operation is RAID-6 and has been reliable. Over the years i have been replacing failed disk drives with models listed on the compatibility chart, and now I find I have three Seagate drives and three Western Digital drives.

Looking at the health report for the individual drives, it seems the number of "Load Cycle Count" roughly matches the number of "Power Cycle Count" for the Western Digital drives ( this makes sense to me, if a load cycle is bringing the heads from park into operating position each spin-up).

Strangely each of the three the Seagate drives are showing a hugely greater number of "Load Cycle Count" than the number of "Power Cycle Count". I have attached a screen-shot of this display.

Is this due to some SMART reporting incompatability with the Seagate drives, or is something else here for me to learn?