Have you checked for slugs? Or snails??

Same thing has happened to me. Entirely cleaned almost every one of them of their flowers in different areas of my garden. I don't see signs of slugs. I read on-line someone caught mice eating them.

Have the "pests" been eating your geranium flowers as well, because I have noticed mine are not flowering like they usually do.

Deer love Pelargonium flowers, but seem to ignore my hardy Geraniums. That's why I don't grow any Pelargoniums. My neighbor does, and they're stripped every year of blossoms.

I just caught a cheeky chestnut backed chickadee eating my lobelia flower buds. And when I went outside to chase him away, he just kept going to town, having himself a hey-day! Cute, but really? I wonder how long this has been going on, as it's the first time I've witnessed it. I put some seeds and peanuts in a dish for him to keep him happy and away from the new little buds. I hope this helps.