This happened to a single bud on mine at 8 weeks of flowering. I followed the advice of @Hammer and plucked it out. Things healed up nicely and, life went on. I think you most surely have bud rot. Check this post out. A good discussion about it (bud rot) and, some resistant strain advice. Bud rot/mold photo I shake the dew off of mine daily now. The buds are full and they get and stay wet. Here is a picture where a rotten bud was removed 3 days ago…
corn borer
Here is an attempt to show where a worm entered at veg stage.
“entry point”…
Even though I killed it with this info How to kill corn borers in my outdoor marijuana garden? it left a path for the rot as mentioned in the “Rot” discussions.