What it is
The lock is the inner mechanism that stops a person from extending love they clearly already have. It’s usually made of a few parts: loyalty confusion (“if I’m kind to him, I’m betraying her”), suffering scripts (“in this family we don’t let things go”), identity protection (“I’m not the one who apologizes”), or reciprocity expectations (“they have to go first”).
Find which part is holding, and the lock often opens on its own.
How it shows up for me
I’ve had locks with people in my own family for years. What opened them was never more love, I had plenty. It was naming the piece that was jammed, usually pride dressed up as principle.