When I type a character it shows up several places back to where the cursor is. The same happens if I hit enter, delete or backspace making it tricky to edit the text to test the font. I’ve noticed this has been happening when I double click on a component to edit it. It’s been going like this for like a week. At the moment of posting this, I had the latest version released.
Try the latest beta please. Go to Glyphs > Preferences > Updates, activate both checkboxes and press the Update button.