Support gap too wide, causing model to lift off the supports- Or the bottom and sides warped up, causing them to bow inward and buckle that thin section.

I agree with other commenters, this seems like turning it 90 so the back face could sit flat on the build plate would likely have a lot better results. If that is not an option, lower the support Z-gap and increase the support interface layer density/decrease line spacing. Make sure your filament is dry. Decrease your cooling fan speeds.