/home/yunohost.app/peertube/ seems to be a leftover from a previous installation.
It should probably have been removed when the original install was uninstalled.
When the new install was run it created a new peertube user which received a new ID but the directory was owned by the old peertube user ID. Hence the permission problem.
I just removed /home/yunohost.app/peertube/ and then the installation went fine. Thanks a lot for helping out! 