Last year I had 0 of these. This year I have over 50. This week finally a flower has appeared, yet I still cannot figure out what plant this is. I am usually quite proficient at plant identification so this is driving me nuts!
Thank you for contacting Toronto Master Gardeners about your mystery plant.
While the photographic image is somewhat blurry, the plant appears to have hairy gray-green leaves, with a soft pink bloom emerging. We believe it to be Lychnis coronaria commonly called Rose Campion, a short-lived perennial or biennial. The Missouri article describes its bloom as magenta, however, there is also pale pink and a white version.
https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=p840
This charming plant is a prolific self seeder, so 50 of these plants in an area is comprehensible since the small seeds could have arrived courtesy of birds or some other wildlife. You may wish to remove some plants before they self seed in your garden. In the meantime, enjoy your lovely volunteers.