My Joomla-platform has a problem with handling the '-character.
Problem was caused by '-characters in map name, e.g.: "2018 GR Melano - Porto Sant'Elpidio"
Had to change to "2018 GR Melano - Porto Sant`Elpidio"
Possibly co-existance problem with an other extension's system-plugin specific on my Joomla system....