I've seen a lot of cosmos around recently. It thrived in the wet and warm temperatures this autumn after an overly scorching summer, I think.

It's worth bearing in mind that plants bloom to reproduce themselves, and if they are too comfortable then they don't feel they *need* to reproduce in order to ensure species survival; the seedlings that germinated for me during the heatwave were so stressed that they rushed into bloom when they were still tiny compared to the previous generation, and were over almost at the same time instead of providing the intended succession of flowers. Depending on the local climate, your non-flowering cosmos may well overwinter in its current state and flower early next year, and the flowering one will die off once it has set seed (or flowered and failed to do so).

Lately, I've received comments on so many of my fanfics, especially on old ones

I'm tempted to say unhelpfully that this is a nice problem to have ;-p
But not if it leads to stressful expectations...