Saturn 4 Ultra 16k - why are some of my prints warping mid-print?

Those droopy sword blades are almost always a support problem, not a layer settings problem. Long thin parts hanging out over nothing need supports that actually reach the build plate, not little tabs floating off the nearest surface. Auto supports on most slicers tend to chain everything to the model itself or to other light supports, and a long thin cross-section just flexes mid-print and sets in the bent shape. I run into the same thing with antenna bits and rifle barrels untill I started manually adding a few medium supports that go all the way down to the plate, plus some cross-bracing between nearby tips so the whole group stiffens up. Once I did that the sagging basicly stopped.

Orientation matters too. Anything long and skinny shoud be tilted, usally somewhere in the 30 to 45 degree range, rather than printed flat and horizontal. Flat horizontal blades give you a big thin pancake of resin curing layer after layer with a huge peel force on every pass, and that is exactly when you get the bent and melty look you are describing. Tilt it, support the low end and the high end, brace the middle, and it holds shape. Your 65F basement is worth a look as well. That is on the cool side for most standard resins, and cold resin prints weaker and more flexible, which shows up worst on thin overhangs while chunky parts still come out fine. That matches your symptoms pretty closely, the failure only showing up on the delicate bits and only sometimes. A small space heater or just moving the printer somewhere warmer for a test print would tell you quickly. Some people also warm the resin bottle in a bucket of warm tap water before pouring. On exposure, the stock profile is usually close enugh that you would see other symptoms first, like failed details or stuck-on prints, before you would see sagging. I would fix supports and orientation first and only touch exposure times if problems remain after that. If you want, post your settings and the tilt angles you are using, but I would bet this gets solved before you change a single number in the exposure fields.

Same mystery on my end for weeks until I got one of those little aquarium thermometers and stuck it to my vat. Turns out the room thermometer lied, the resin itself was sitting way colder than I thought. What fixed it for me was a seedling heat mat from the garden store, the kind for starting cuttings, sitting under the printer. Cheap and it keeps things steady all winter. Also worth checking when the droop happens in time, if the parts are straight when they come off the plate but bend after washing, that is a curing problem not a printing one. Thin flat pieces warp while curing if you lay them down. I stand mine up against a jar in the cure station now and that solved a batch of bendy spears I blamed on supports for months.

Seconding the resin temp thing. I kept a little strip thermometer on the side of my resin bottle for a while and it was consistently 8-10 degrees colder than the room, sitting on a shelf against an outside wall. Once I started stashing my bottles on top of the water heater cabinet instead, the floppy thin parts basically disappeared. Looks like a wierd place to store resin but it works. Worth checking where the bottle actually lives between prints, not just where the printer is.

Total beginner here so take this with a grain of salt, but when I had this on my old Mars I blamed the print and it turned out my curing station was bending them. Thin parts heat up in the cure station and sag if they're leaning against the turntable or each other. Now I lay small pieces flat on a mirror tile instead of standing them up and the problem went away. So maybe check wheather the parts are alredy bent when they come off the plate, or only after washing and curing. That would tell you if it's even happening during the print at all.