Please can you try:
cd /var/discourse
./launcher enter app
ls -l node_modules | grep ember-source
It should produce something like
# ls -l node_modules | grep ember-source
drwxr-xr-x 9 discourse discourse 4096 May 2 00:23 ember-source
drwxr-xr-x 4 discourse discourse 4096 May 2 00:23 ember-source-channel-url