In case that the display of your aXbo shows all symbols, a reset could fix the problem (see article: Reset your aXbo).
In case that display of your aXbo shows weird icons indicating in certain cases, a firmware upgrade might fix the problem (see category: Software & Sounds).
In case that your display is not showing some symbols, a cleaning of the contact surfaces of display/conductive rubber/board will fix the problem (see article: Individual icons are not displayed).
If this didn't solve your problem, please submit a request.