sometimes when i close and reopen my client chest the items i just put in get deleted

I haven't experienced this; can you clarify a few things?

• How are you placing the items in the client chest? (shift+clicking or normal clicking)
• Are you closing the client chest immediately after placing the item? How quickly are you reopening the client chest? (Neither of these should cause this, but it might be)
• What Minecraft version are you using?
• Are you in creative or survival?
• Is locked slots enabled? (This is also forced on while in survival)
• Are you using the small client chest or the large client chest system? (/nbt config, small is default)
• Are these items always large? (in terms of data size, lengthy strings, etc.)
• Do any errors appear in chat or the logs?

I'm assuming you're using the latest version of NBT Editor.

In the meantime, if you're clicking (not shift+clicking), then the deleted item should be recoverable in the /get lostitem history. This opens a gui with the last items contained in the cursor.