If it's pre-'13 and you're getting a long crank with no drivability symptoms or lit MIL, the crankshaft sensor (CKP) is your most likely culprit. They often get weak at cranking speed but start signaling normally once the engine catches and the reluctor is spinning faster, so no code gets thrown.
So, 2018 would be an R52 series with a 3.5L-V6 (not a 3.5). If it's under 60,000 miles, it may be covered under warranty, so you should check with your Nissan dealer. You can also have the codes checked; many auto parts store will check powertrain codes for free. Crank position and cam position sensors can sometimes start to fail and cause those symptoms and not always set a trouble code.