Why does my print turn into a droopy stringy mess halfway through?

That collapse mid-print is super common, and while temprature is a major factor, you need to look closely at how your slicing settings interact with that drop in temperature. The 'melted cheese' look usually points to either curing too aggressively or the structure not being able to hold its own as it shrinks slightly during the build. The cured floaters in the vat are a good sign that the resin was working, but that doesn't mean the part itself was stable.

If you haven't adjusted anything, the default settings might be too fast for a complex geometry. When the print starts to get taller and the part is under its own weight, if the lift speed is too quick or the exposure time is too long, the newly cured layer might pull away from the layer below it instead of bonding. Think about it this way: if the light cures the part too hard, it becomes brittle, and the slight movement of the print platform or the subsequent layers just break the connection. Try reducing the exposure time slightly and increasing the lift speed just a hair. It sounds small, but it makes a difference in how the resin flows back. As for the cold, the garage enviornment is definatly making it worse. Resin shrinks a bit as it cools, and if the temperature drop is quick, that internal stress can cause the whole thing to lose structural integrity. You don't need to heat the garage, but try insulating the printer or running a space heater nearby just for the printing duration. Maintaining a stable, warmer environment helps the resin cure more evenly and reduces micro-cracks. Finally, about the plate: since the first layers were solid, the base leveling is probably okay. But if the print failed due to internal stress or poor layer bonding mid-print, re-leveling won't fix the root issue. Focus on those speed and exposure settings first. The stringy bits are just a symptom of poor layer adhesion, not necessarily a leveling problem.

I agree with the point about how aggressive curing causes that structure to lose its grip when it gets heavier. When I started seeing similar failures, adjusting just the exposure time wasn't enought. I had to tweak the vat tilt slightly while I was dialing in the new settings. Running the printer with a minimal, consistent tilt helped level out the resin flow between layers, which stopped the stringy bits from forming even when the part was huge. You might want to try that adjustment alongside the speed changes.

I had something like this happen with a bigger model once. Smaller stuff printed fine but anything tall just turned to goop halfway. Turned out the little window where the light shines up through had a smudge of dried resin on it, so parts of each layer weren't getting enough light. Wiped it clean and the next tall print came out fine. Does yours have a screen like that under the tray you can check?

You gotta check your resin viscosity. Sometimes the resin just gets too thick or clumpy, especally if it’s been sitting around. When that happens, the layers don’t spread right and the whole thing just starts losing adhesion even if your settings look fine. You remember back in the day, we always had to stir the mix thoroughly before we poured it, right? It's the same idea, just on a smaller scale. Have you tried a fresh batch, or just warming up the current resin a bit before the print run?

One thing I'd check is the transition layers. That failure point about a third of the way up lines up with where the bottom layers hand off to normal exposure, and if that ramp is too short the layer bonding takes a hit right when the part starts getting heavy. On my printer I run 8 transition layers instead of the default and it fixed prints that used to snap off at the same height every time. Also grab a cheap thermometer and stick it near the vat overnight, my garage was sitting at 12C when I did that and the prints told the whole story.