Hey if you see this can you answer one more question:
How much abuse was your high availability product delivering to these cards in terms of writes? Was it something like a video recorder, database, cryptocurrency, or some other application that did large amounts of write I/O?
I ask because we're about to ship something that uses SD cards, but the I/O is very low. It's a network appliance and doesn't do anything locally that is high write throughput.
We weren't beating up the SD card with heavy writes. It was for a robotics controller, so just sort of normal, low throughput logging.
We even saw SD cards screwing up in RO mode in fact, from major brands. Trust me, you want to swap out for an industrial card in your BoM.
Have you tried things like jffs2? Do they help?
Even the brand name cards aren't worth shit; you need to buy "industrial" cards.
Source: tried to get a root filesystem to work on name brand SD cards for a high availability product.