Hi,
Welcome to the RStudio community!
This sounds like a file encoding / display issue. The fact that it works locally is probably because some background settings are different. If the input files are not in the correct encoding format, then some may only display on certain machines.
I found an article that might help you here. To check what your default encoding on your machine is, run localeToCharset(). ShinyApps usually runs with UTF-8 so if the format is not correct, it might read it incorrectly. You can always read data with specifying the encoding explicitly, or save it in UTF-8 so it'll default to the correct one.
Finally, you can change the R environment by using the locales as described here.
Hope this helps,
PJ
.