Fatal error: Array and string offset access syntax with curly braces is no longer supported in media/k2/assets/vendors/verot/
need to be addressed in all new releases. Replace the string curly braces with square braces on that line.
Otherwise you get a blank page (fatal error) when you add or edit an K2 item ans press "Save" or "Save and close" and the item is not saved in database.

The culprit file is /media/k2/assets/vendors/verot/
I donno why but it seems that i cannot save this update in the initial message.