I’ve got same problem since May 2019. Have been doing loads of tests with generic and 3rd party resins, but nothing helps… Latest info from Zortrax via retailer was, apparently temperature difference when parts lifts up from resin vat…
I slowed printer down, exceeded exposure time, exposure time off too, run parts hollowed and solid, made thicker supports (2mm), bigger tips (1mm), longer tip (3.5mm) that helped a bit, run with tips ball or without, re-leveled whole printer, platform leveled every-run, platform was sanded due to uneven surface, I pre-warm resin and keep temp between 22-24.5C (winter) and during summer 26C+ and results were same, few months ago replaced LCD, but it’s same. Reasonably good results I have with organic shapes - they still get that sagging, but it’s not really visible and sanding helps. Precise and sharp egdes (even with filets) getting deformed.
I think it’s mechanical or LEDs are no good, but I can’t get this solved for over 6mths.
If you find solution let me know as I want my printer finally start making good parts.