A print can finish even if some parts of the object weren’t printed fully, though a missing part of an object will more often cause the whole print-job to fail. Try printing a sample object to see whether it is also affected by this issue.

Lack of supports
Please check the SL1 Handbook, chapter 6.5: Slicing objects for the SL1, to learn how to correctly position an object and generate supports for it. Keep in mind that parts of the object cannot start mid-air and that the printer has a threshold for overhangs.
Incorrect exposure times
If you set incorrect exposure times (especially too low times), the resin will not have enough time to solidify, which may result in missing details. Always make sure you’re using recommended exposure times for your prints.
Faulty hardware
Another possibility (a less common one) is that your print display or UV LED panel is faulty, so either the mask is incorrectly displayed or only a part of the object is cured by UV light. Please contact customer support if the previous steps did not solve the issue.