Normal should be around 7-10MB/s for your card. I mean with the low resource limitations that a bootloader imposes.
So I have a class 6 that is faster than yours. So your card may need different configuration.
First of all, I need a screenshot of the Console Info -> Sd card info.
This ^
Did you boot into Horizon OS in between the two full NAND backups made with 2.1? Booting into Horizon OS, even if you turn it off immediately after, that will make slight changes to your NAND.
Now that you say that i think i did that. Im doing 2 more backups right now with version 2.2 without entering Horizon to see if this time it goes well, thanks!