I gave tech support a call about this disappearing journal question. One thing to check is to see if you selected the "white" ink for the pen. When you write with white "ink", the Journal will display a black line initially as you draw (it does this for faster response). When you refresh, switch or save the page, the Journal redraws the page with the actual colour in high quality. At this point, the ink changes to the actual white colour, and therefore can disappear if you're written against the standard empty white background.

To check or change the pen colour, show the "Menu" at the bottom of the Journal, then tap the menu item to the left of the "Help" menu (if you have "White" selected, it will show that as the menu caption). Simple select another colour, such as "Black". Now when you write, it will still appear black at first, but when you refresh the page, move to another page, etc., it will stay black.

Hopefully this helps