Lychee is a free photo-management tool, which runs on your server or web-space. Installing is a matter of seconds. Upload, manage and share photos like from a native application. Lychee comes with everything you need and all your photos are stored securely.
I think that somehow your server is retrieving an old version of the app (I have just had a similar issue). The correct version should not ask you for a password, for example.
Uninstall the app.
Try updating your catalog: yunohost tools update --apps, then install it again.
Try installing it from the command line ? yunohost app install https://github.com/YunoHost-Apps/lychee_ynh --force