So, I think I got to the bottom of this - it was under watering. It was also quite warm inside my hooped garden so I suspect the heat, combined with dry conditions, caused the leaves to burn.
My strawberries are planted in raised rows. When I watered them, the water was not seaping into the middle of the mound. I was too concerned with over-watering.
I removed the cover, have been watering more. While one plant died, all others are doing better and most of my bare-roots have leaves now.