I had that happen. I can't tell you what happened as my dog decided to help me prune her and she ate the whole fucking plant. I had one of those and one that split into 2 tops from the beginning.
I have a medical strain now that went 3 on the 4th, skipped the 5th, than it's been 3 on all the rest. Making it pretty bushy, and I'm having to tie some greenery back.