I have a focus bonsai that has lost over 50% of it's leaves already. Both fully grown and budding leaves are turning yellow and dropping.

Couple things I noticed:
There are cobwebs on the tree
There are little black beads on some leaves that I can remove easily
Some leaves are stained with black dots

All leaves turn spotty yellow and then completely yellow and die.

It seems like it has like 50 problems, am hoping someone can help diagnose...

I have been watering it once a week or twice a week, so likely overwatering vs underwatering.

Couple more notes:

It has turned cold in SF and my apartment has dropped maybe 10 degrees Fahrenheit. It is also a bit drier here

Possible spider mite infestation, hold a white sheet of paper under a set of leaves and shake, look for flecks of black or red specks that move. If confirmed then spray with insecticidal soap focusing on the underside of the leaves.