Odd. Perhaps it is related to skipping so many versions. Not sure. But we need to try something more drastic 🙂
Close your browser.
In your database find the kiwitrees “xxx_session” table. (where xxx is the prefix you use to differentiate between kiwitrees and webtrees tables). Make sure it is the kiwitrees one! Delete all the rows in that table.
Now try restarting your browser
EDIT: You will probably need your browser open to access the database! But closer it after modifying the table, then restart it to access kiwitrees.