Set the warm, room temperature cream cheese in the bowl of a stand mixer. Use a rubber spatula to press it into the bottom and sides of the bowl to remove lumps. Affix the paddle attachment and turn the machine on its lowest setting to gently cream the cheese. Scrape the bowl down as needed and mix until the cream cheese is smooth.
Add the labne/sour cream, sugar, vanilla, cinnamon if using, and fine sea salt and turn the mixer on low again. Mix for about 5 minutes, until the batter is smooth. Scrape down as needed.
With the mixer on, add the eggs and mix to just combine; about two minutes. Scrape the bowl’s sides and especially the bottom to ensure everything is well mixed.
Pour half of the cheesecake batter into the pan. Dollop the rhubarb sauce (in 2-3 tablespoons) all over the cheesecake. Gently shimmy the pan on the counter so the filling evens out. Pour the rest of the cheesecake filling, do it in dollops so that you’re able to cover the rhubarb. Dollop more rhubarb sauce on top. Use a chopstick to gently swirl the rhubarb and cheesecake batter, 2-3 full swirls should do it - don’t overdo the swirling.
Set the pan in a larger cake pan and fill the larger pan halfway with water. Turn the oven down to 325 F and bake the cheesecake in its water bath until the middle jiggles just a bit when you wiggle the pan - about 45-50 minutes. *If you don't have a bigger pan to turn into a water bath, set a pan with water on the rack underneath the cheesecake - this isn’t ideal but will work in a pinch, please note that the cheesecake will likely cook faster if not submerged in the bath.
Turn off the oven and leave the oven door open so the cheesecake can begin to cool. After about 15 minutes, take it out (still in its water bath) and leave it on the counter. When the cheesecake is cool enough to lift out of the bath, set it on the counter to cool fully then transfer to the fridge. Chill overnight, or at least for 8 hours.
Store the cheesecake in the fridge, it’ll keep for about 5 days.