Added text does not line up with existing text in Pages

I wonder if anyone has a solution to this problem that has recently emerged. I'm writing my thesis in Pages which I prefer to Word. Broadly it's great, but I'm experiencing a problem with editing. I frequently need to add new text as I refine my writing. The new text now consistently appears a notch under the existing text. See example: "It is important to note that..." "That" and "the" on the first line aren't quite level. It's pretty subtle, it's not very serious in the scheme of things, but it's maddening once you notice it.

I have tried saving and re-opening the file in case it's a glitch on the screen, but it seems to be a problem in the Pages file itself. I'm using Version 11.1 on a 2018 mini.

The only solution that works is a bore: I re-write the whole the line, erase the text that was there before, and the problem becomes invisible.

Thanks in advance for any observations...