if i double click on the graph instead of the edit graph pop up window, it appears a small light blue rectangule instead, i can type anything in it
basically the grapf has lost all data connection and show values and lines as a fixed pic
If you copied or cut and pasted the graph AND you use a third party clipboard manager (some Linux distributions include one activated by default) then the paste might be an image IF the clipboard manager doesn’t use/retain LibreOffice formats (quite likely doesn’t).