We already went through underwriting and are in process of finalizing our loan. Our appraisal is next week and our LO emails us today asking for our landlords number address ect and says they will not call him until they have our permission?! Well they already have all the checks that we payed rent with so why call? I just sent him a message with his info. and told him that we prefer they don't call him until we are almost moved out of here or we will have possible future tenants in and out of this house and we have small kids. We have always dropped our rent in the dropbox/mailbox at his office anywhere from the 1st to the 8th and its due on the first. But the landlord cannot prove that we were late because we did not personally hand the checks to him.
I'm guessing that you probably went through automated underwriting and now they are pulling your file through manual underwriting to make sure everything is as it appears. This is a normal process.
Also, I don't know how it works as far as what your landlord has to say about your payment history. Is this a special condition of your approval? I would think a bank statement or cancelled checks would be better proof of payment. Either way, payment on the 8th should still be considered on time. I think they are more looking for non-payment or 10+ days late. Your best bet would be to ask your LO. In my experience, the LO is there to help you, not hurt you - and it's best to be honest with them about any concerns you have.