I don't own any JLP, so I'm not 100% sure, but I think that it acts kinda similarly to those tokens know as "yeald bearing token", where the earnings aren't used to mint new tokens (which usually are then ditributed to the holders, who see their number of tokens increase) but are used to increase the token's value: so, intestad off seeing both your balance of tokens and total value increasing, you only see the total value growing, as every single token become more valuable with time.

That would explain why you weren't seeing your JPL balance growing, while their value was :)

I was told I needed to use the JLP multiply

With "multiply" you can do that trick (deposit, borrow, swap, deposit, etc) with one single tx: much quicker and easier! Same if you want to deleverage your position.

You can check my post for a brief introduction of the feature :)