The multisession function works for CDs, but not for DVDs.
There is no option to add files after creating a Multisession DVD. Why is it not possible to create a multisession DVD with brasero?
When burning it there is an option called Leave the disc open to add other files later
Click on Properties And the following Windows will appear:
Other users have reported that turning on DAO in Edit > Modules > growisofs > Settings also helped.
Lastly it also depends on the DVD Recorded you are using. Some models have been known to create this problem. Changing the unit helped.