Hello, upstream dev here.
I think it can related to the XDG folders that are set to something outside of the user ownership (like /usr/share for example) Can you check that Remmina is not trying to save where your user doesn't have permissions to write? From our point of view, having Remmina using profiles inside folder without writing permissions, could be normal and we ignore the exception, this is to allow admins to distribute profiles to the users and avoid that they could modify those profiles. That said, start remmina from the command line and look for any interesting messages if any, than start again but set the XDG folders in advance (export XDG_xxxxxxx=$HOME/whatever). I'm mobile at the moment so I cannot check easily the XDG folder names. Please plet me know what happens than.