There can be just two possible causes. One, the curing time for the first few bottom layer was to short. Two, would be a build platform that is not leveled correctly.
As a part of first problem is the fact that Uniz Desktop slicer only makes three bottom layers which might not be enough. Still in the same department is the fact that the very first layer is not wider that the next layers. The first layers should be like “elephant foot” or brim or raft as an analogy with filament 3D printers.
So the solution would be to use either another slicer that is capable of making good support (Meshmixer, Chitubox, etc.) and then import the STL from it… or increase the curing time for those first three layers.
Also recheck and redo a build platform leveling procedure with a sheet of paper.