iOS 13 is out by Apple and it does break a few things unfortunately. If you have upgraded your iPhone to the latest OS and especially if you are running the Dark Mode setting, some of the text in the app will not be legible.
Fear not, this is a temporary issue and will be shortly resolved. I'm working on version 9.0 that will not only fix the issue but will also allow you to run the app in a brand new Dark Mode mode (looks great when you are entering your parameters in dark basement).
Thank you for your patience, this will be released very soon. Watch out for 9.0, it was submitted to the App Store today.