Fallback rise?

Tara • Mama bear to an angel, 4/5/17, born after 34 amazing weeks and a son born 11/15/18.
Hello all! I'm 3DPO today, and had a significant temp drop, back down to coverline... Anyone know more info on fallback rises? It's way too early for implantation, and I'm 99% sure I ovulated, with a positive OPK and CM. any thoughts? I'll post my chart below.