@Michael Solomon congrats on what seems to be a successful house hacking journey.
Here's how this works. The lender is going to require your most recent tax return. If a property was placed into service as an investment property prior to that tax year, then the lender is going to calculate your qualifying rental income (or loss) from your Schedule E. (If there is no rental income listed on your Schedule E in that scenario, you cannot use any rental income, period, even with a lease.) If the property was placed into service as an investment property during that tax year, and there is partial year of rental income, make sure that you put the correct number of fair rental days on your Schedule E, and the lender will prorate it for a full year. If the property was placed into service as an investment property after that tax year, that's when we can use your lease, and we use 75% of the rent and wash that against the PITI (total mortgage payment).
So in your case, by the time you are ready to buy your 3rd property, your 1st property will be using your most recent tax return for your qualifying rental income. Your 2nd property will be using a lease, since you would be doing what's called a Conversion of your Primary Residence, which is when you buy a new primary and convert your existing primary to an investment property at the same time.
Hope that helps. If you are working with a lender that does not underwrite to these exact Conventional guidelines, run. And based on your questions, it sounds like the loan officer you are working with isn't doing their job coaching you, mapping out your game plan, and explaining all of this.
TYFYS and best of luck!