zsh scp completion of remote files doesn't work when running SSHHelper
The culprit is android's crippled ls command. Zsh's completion run ls -d1FL which /system/bin/ls doesn't understand. 

A way to fix this is to edit /data/data/com.arachnoid.sshelper/home/.ssh/environment such that /data/user/0/com.arachnoid.sshelper/bin is the first entry in PATH. (SSHelper ships with a more complete ls)

Note that SSHelper might rewrite this file on updates?