Changes don’t save

Hello

I have a weird and annoying problem. Nearly every time i change a thing on map, it says "It seems someone else have modify the map. You can continue saving, but files will be lost". If i click continue, it doesn't save anything at all, if i quit and return, the things i add aren't here anymore.

I'm the only one to work on that map. I give me right to modify in the permission tab. I'm always connect with my openstreetmap account.

So i really don't understand where that bug come from. Can someone help me to solve it? I can't do anything until it's solved as it doesn't save anything.