That’s strange. My locale is german, there is also a comma instead of a period in the decimal number. I don’t have this problem. Following shortcode runs successfully on one page, in english as well as in german:
[leaflet-map fitbounds]
[leaflet-marker lat=44,67 lng=-63,61 title="test"]Test[/leaflet-marker]
[leaflet-map fitbounds]
[leaflet-marker lat=44.67 lng=-63.61 title="test"]Test[/leaflet-marker]
[leaflet-map zoom=11 address="Liessel,Noord-Brabant, Nederland"] [leaflet-marker message="Liessel" visible]
My next idea: Clear the geocoder cache.