If your browser appears to be having trouble displaying all of the information on the page or is preventing you from being able to save changes, you likely need to perform a Hard Refresh on that page. An example of this can be if it makes your textbox look like a string of code instead of English.
The keyboard shortcuts for a Hard Refresh differ depending on your browser and computer. Refer to the photo below and use the steps that apply to you on the page where you are having the issue. After performing the Hard Refresh, you should be able to make the changes you want and save without incident.