LINE Letter Sealing - Unable to display message as it couldn't be decrypted LINE is a chat application.

I recently reinstalled my OS, and restored my LINE chat history using this procedure.

Problem: Some of my chats appear like this:



It says:


  Letter Sealing
  Unable to display message as it couldn't be decrypted. Please ask your friend to resend the message.


As you can see, my friend re-sending me the message does not solve the problem.

On the messages from July 6 to the day I reinstalled have this problem.

So I disabled Letter Sealing, and now I can read new messages sent to me (but I can still not read the existing problematic messages).

Questions:


How to make the problematic messages readable again? I still have the Titanium Backup from the former OS, if necessary.
Is there a way to re-enable Letter Sealing while making sure that encrypted messages will stay readable even after reinstalling my OS in the future?
Had the same problem. The second method on this page worked for me.

Steps:


Do a previous backup
copy /data/data/jp.naver.line.android/databases/naver_line to your PC and rename it to naver_line_old
Reinstall and do a fresh setup of LINE
copy the new naver_line to your PC and rename it to naver_line_new
In your PC, open and copy the chat_history table from naver_line_old(I used SQLiteStudio) and paste it on naver_line_new, having previously deleted chat_history from it
copy naver_line_new to /data/data/jp.naver.line.android/databases/naver_line(rename it as naver_line)
Restart your phone


Letter sealing should work OK now; unfortunately, I don't know how to make the problematic messages readable again.

I hope to have solved your problem.