The splitting at the base is usually due to undercuring of the first layers or undue peel force during the printing. These layers are overcured intentionally to promote bonding to the build platform. However, the resin is still “green” after polymerization and, thus, structurally weak. Failure along layer lines of the base can be a symptom of overloading.
I am guessing that the problem is the peel forces due to the size of your model. I suggest reducing the PM setting to try and reduce the draw force. Also, is the model hollowed and vented? Improper venting will increase suction forces and can damage the print.
As for movement in the vat, it should not be an issue as long as it doesn’t move during the polymerization phase. Some movement during the peel phase is expected, as even the FEP will flex under load.
I have one last thought: have you tried (do you have) the original build plate? I am wondering if you are experiencing shifting in the easy-level build plate, which is also damaging the model.