Ordering the services doesn’t work (and makes me crazy)

I have tried a lot of different things trying to order the services.
Including contacting Salon Booking, but because I am testing on the free version of the plugin prior to persuade my client that this plugin is the good one and she has to buy a license, their only answer is “it word on our demo server”… !!! Guys, this is not the way to help your users !!

I have tried to order the items by drag/drop on the backoffice : one item stay at the first place and wont move.

I have tried to look inside the database to ensure that the fields contain effectively the order, found that it uses  _sln_service_order, and been able to see that the items have the good order…

What is also crazy is that I have tried to change the name of the one that want to stay in the first place, so I have rename each item… And guess what? At the time I rename the last one with the text, it goes to the first place.

Here are the 3 text items I am trying to create :
Séance de Psychothérapie
Séance de Neurothérapie (évolution EMDR)
Séance de Lithothérapie

And for an unknown reason, the item “Séance de Lithothérapie” always want to stay at the first place !!!!