Starting the installer fails on ppc64le because there is not enough free space in install.img filesystem. The compose's program.log says it's only 10MB (x86_64 reports 140MB free). The symptoms a "no space left on device" error.
df says 4K free on /dev/mapper/live-rw
tested with Fedora-Rawhide-20190115.n.0 (and previous)
The solution is to increase the install.img size to 3GB from the default 2GB. The main question is where it should be changed. In lorax directly or in the compose configs in pungi, globally or per arch. Maybe there is something we could remove in lorax in runtime-cleanup, but it would be a very temporary solution.
ACK, Dennis Gilmore made a good point that having a bigger image by default could have negative effects on the low memory / 32-bit platforms, so better to go with pungi config change.