In octocitrico.sh
the line
OCTOPI_TAG="0.18.0"
refers to
https://github.com/guysoft/OctoPi/tree/devel/src/modules/octopi/filesystem/home/root/bin

In devel Branch of this repo there are new changes to install mjpeg-streamer w/o user names.
These changes are not in octocitrico. That's why mjpg-streamer installation doesn't work with modified user.

One example_ In webcamd, the line MJPGSTREAMER_HOME=/opt/mjpg-streamer differs.