In a file you shared, there's no curve set at all.
Still, it works as it should.
Once a custom curve is defined, it renders straight to PV w/o any problems. And doesn't reset even after restart.
W10, R18, CRN 5.2 here, so maybe it's just Mac...
example: Curve On vs Curve OFF
Modified scene w/ results attached.
//
& Damn, now I wish I could animate curves and all postFX, passes, lights... with/in Corona VFB. The team should really oughta make a standalone Studio Compositor version :p