The original initramfs warning looks like it is an Ubuntu error. See:
- https://forums.developer.nvidia.com/t/warnings-with-update-of-initramfs-tools-to-0-130ubuntu3-10/154462/7
- https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1800719
I couldn’t tell you why the one SD is faster than the other. Samsung SD cards tend to work correctly from my experience, but there is a lot which can go on and change this. I don’t know how to debug SD card speed issues.