If see an exclamation mark ! instead of a number in a graphic display, it means the number is too large to fit in the field size for the tag. For example, the display digits (integer) is 2, but the value is 101, three digits won't fit inside 2 digits.
You should contact and engineer or technician and let them know the tag name. They will have to use Project Manager to increase the display digits for the tag by editing the tag properties.