Low appraisal on multihome. Need feedback quick!

[Milena Blanch]

I offered 508K on a duplex and offer was accepted, one unit is already rented for a year (below market, we could get more when lease is over) and the ROI and strategy to househack for a few years is perfect for my family to start-off our investing journey, we would be saving a lot on rent. However, the appraisal just came back at 450K. I talked to my lender about numbers and we're going to start the negotiation at 460 but the lender gave me the numbers at 495 (asking price was 500K) and mortgage still makes sense. I know the market is crazy, and the numbers looks good but offering 45K over appraisal value? The sellers realtor said they had a cash offer after our contract was signed, we don't know if this is true but even so is this the new normal for a multihome?