A pic would really help, hard to say w/out one. SOUNDS like a drainage problem. Would have been especially helpful to see the roots when you repotted.

Can you pls describe what the roots looked like? Does the pot have a hole? What kind of soil are you using? How often are you watering? Sorry for all the Qs, but your description is really insufficient to diagnose this.

Or could be old leaves.

Should I cut them off or leave them?

Either. When the leaf turns completely yellow, it will easily snap off at the vine. If you try to snap off a green leaf, it may damage the node (on the vine). Eventually the leaves will turn brown and may or may not fall off on their own. If you don't like the look of yellowing leaves, snip them off close to the vine. Then wait a few days for the remnant of the petiole to dry up and you can rub it off with your fingers.

Thx for adding the pic, but showing us failing individuals leaves doesn't help assess the WHOLE plant, pls consider what you're asking.

Could you pls show the entire plant & the soil & the pot?

Why did you Ebson Salts? If you did it together w/ the Fertilizer, that may have been more than the plant could handle.

Is that a moss pole of some kind in the Center? Could it be rotting?