If your splint calculation unexpectedly closes, it is most likely due to the presence of two or more margin lines causing the issue.
Please remove the additional margin lines to ensure a smooth calculation process.
Note that splints typically should have only one margin line.
The problem might have occurred, during the CAD process, you designed the margin line above the gingiva and then extended it into the depth of the gingiva in the "Design Bite Splint Top" step, as shown in the attached image.
To avoid such issues, We recommend adding more control points to the margin line, as illustrated here.
This should effectively resolve the problem.
If you need further assistance or have additional questions, we are here to help.