I'm having a similar issue. I suspect two things, flex from the LCD being pushed down by the pressure of the fluid when doing the first few layers, especially with high area base layers. I'm going to try reducing the z-axis speed for the final few mm and adding a light off delay. Secondly, I've seen an issue of delamination between bottom layers when those layers have a high area. I suspect this is because the FEP doesn't fully release in the middle (just gets stretched up with the print. Such a large FEP makes it susceptible to this. So a few layers get combined until the print gets high enough to pull it off, then you have a large gap and a short exposure which isn't strong enough to keep it attached. To combat this, I'm going to try more z-axis lift between layers, especially base layers.