Font size changing in CC in 2017

I'm using Captivate 2017 with a custom theme, on a blank project. I copied and pasted font from a word document. I clicked "Don't copy formatting" so it shouldn't have brought anything over from the word document. I have also used a downloaded app to convert copied clipboard text to pure text. I have ensured that the entire project is Arial 18 and overridden individual slide controls so it's all the same. I still have different sized font sizes when it publishes. What am I doing wrong? The example I show below is the exact same slide, one sentence right after the other.