I get it done by changing the SYNCTOKEN_PREFIX form the SabreDav Doc to the nextcloud one according this link :
Hope it helps.
How can this be fixed?
It can’t. If you want that, you have to force synchronization on the phone before you edit the event. In DAVx5, the server always wins and DAVx5 never overwrites data that has been changed on the server in the meanwhile.
In DAVx5, the server always wins. This is not perfect, but it makes sure that there are no “edit wars”.
You can see your scenario like this:
Actual result: DAVx5 sees that the event has been changed on the server and uses the server version because server always wins when there’s a conflict. Unimportant information is lost.
Your scenario: DAVx5 would overwrite important information with unimportant information.
So, in summary: if you want to avoid conflicts, force synchronization in your calendar app or DAVx5 before editing an event.
Thank you for the explanation.