When did this problem develop? Did you buy a new MD-HMI with an older T100MD888+?
If you remove power to the PLC, then unplug the expansion cable but leave the LCD cable, and then re-apply power to the PLC, will the LCD display the character properly? If so, it is the expansion port interface problem with the HMI. Please contact us via email to support@tri-plc.com or phone us at 1-877-874-7527 so that we can troubleshoot the problem with you and try to fix it.