String indicators don't "format" any data, they just diplay it (of course you also have to option of /code or hexadecimal if desired).
I dont use GBIB, but if it is really just a string indicator there are two possibilities:
-- The string data gets truncated somewhere in the code. It could be that the byte count in GPIB read is to small for your application.
-- The indicator is simply too small for the data. In this case you can just enlarge it and even display a scroll bar.
It is difficult to say more without seeing the code. How long is the expected string and how many characters do you actually see?