I had an issue with version 3.4.0-1. When I tried to wipe or flash system partitiion I got following message:
Failed to unmount '/system' (Device or resource busy)
I also could not unmount system partition from mount menu: I touched the tick next to "system" but it kept being marked. Other partitions mounted/unmounted ok.
I tried twrp-3.2.3-0-cedric.img. This one did not have the issue. I wiped the system partition. After reboot I flashed 3.4.0-1 and now flashing works.
The system partition was stock firmware (never flashed yet). Seems like 3.4.0-1 has some issue with stock system partition.