plotOutput producing different res with same input

I've been working on an app that takes as input an xlsx file, reads its contents, and then generates a ggplot image. The ui is here, and the server is here.
An example xlsx file is here.

My problem is that the first time you upload the input file the text within the rendered ggplot image is very small. If you upload that same file a second time, however, it displays it at the readable size I specify if the ggplot call.

Specifying resolution doesn't seem to have an effect.