A few additional things I've tried today:
- Adding boot_delay to config.txt
- Update to linux-aarch64 4.19.2-1 and linux-firmware 20181026.1cb4e51-1
How ever, it didn't change the behavior on my RPi 3b+, RPi 3b still working with the same SD card.
What did work, was flashing a Raspian image to an SD card, with that both of my RPi 3b+ worked --> doesn't seem to be a hardware issue with the RPis or the SD cards?