Maybe stupid, but got used 2 this from FreeNas 9... Needed 2 rummage 4 ssd...
IMHO! The key is this
Something wrong in installer partition table initializarion. IMHO, needed 2 erase all and create new table from scratch, but installer is not doing this. BTW, Rufus install media boots OK, but the error above. I erased everything on sticks in win10 diskpart, but no success. Maybe, needed 2 init GPT partitions before installation? Notebook with ubuntu present...
And! May be important - rufus is too brainy, proposed 2 install a new grub wjile creating megia. May be the cause too