Om Swami
Why does my mind sometimes feel into bhakti and sometimes not at all?
A pure mind engages in bhakti
The mind engages in bhakti when it is pure. The more conflict in the mind, the less it settles in bhakti, and the purer the mind, the less bhakti you have to do.
Whenever the mind is pure, your mind will engage in bhakti. The more the mind is full of conflict, the less it will engage in bhakti.