In case that individual symbols on the display of your aXbo are not shown, it seems to be a contact-problem between the board and the conductive rubber and/or between the conductive rubber and the display or a faulty conductive rubber.
Any contacting-troubles you can solve yourself (see category Service & Repair parts; disassemble, clean all contact surfaces, reassemble and test).
Service parts (in the case: display & conductive rubber) are available at this shop:
www.axbo.com/collections/service