My new geraniums look so healthy and have lots of new growth but it seems that when the buds are growing, the entire end of the stem (with buds) turn brown and fall off.

We've had A LOT of rain lately and some things have grey mold but these show no sign of any problems on the leave.

I did fertilize all my annuals this year (b/c I reused potting soil) with Dr Earth Bud and Bloom Booster.

What could this be?