I believe you have posted this question twice. Rather than make the same post over and over again, you can use post an answer to "bump" your question back up to the top of Recent Items. This can avoid confusion that can happen when different people reply to different copies of the same question.
What you describe is very unusual. Are there any script triggers specified for this layout?
When a record "disappears" is it gone from view but still in the table? (Try using Show All Records to examine all the records in your table.)
This is weird enough that I wonder if your file might be damaged. Perform a recover on the file and see what is reported. Test the recovered copy, even if no problems are reported, and see if the problem was solved by the recover process.
Things to keep in mind about Recover:
- Recover does not detect all problems
- Recover doesn't always fix all problems correctly
- Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.