I notice that another utility, mbrwizard, also shows that the gpt backup partition is "invalid"; something is definitely writing into that area.
One theory I have is that SSDs using unpartitioned (unallocated) space at the end of the drive for manual overprovisioning may be incompatible with the full GPT spec. (perhaps the ssd thinks it can use that location near the very end of the drive, where the GPT backup partition information is, as a scratchpad?).
If anyone with GPT partitions on SSD drives or intel RAIDed drives or both can run mbrwizard, gpt fdisk, or some other gpt-compatible utility, to see if their gpt partitions, both main and backup, are valid (passing crc checks), that would be helpful to know. Typically I see a cycle within half an hour of valid followed by invalid, and it's hard to figure out what is going on.
Any other suggestions are welcome. (chkdsk and raid verification report no problems--only the gpt backup partition is getting corrupted.)