APK downgrade extraction fails on Samsung smartphones

A friend of mine Ellen she asks me to give her a hand. Couple days ago she tried to extract LINE chat history from a Samsung smartphone running Android 12 as below screenshot.

She did check its settings and pretty sure that a special feature called "Dual Messenger" is activated as below. That means there is an original one LINE and a second one on this phone.

During extraction everything seems fine~ Backup is completed and all split apks instaalled without fail. To her surprise she got only 1KB android backup file. Definitely no chat history in this backup file.

What makes matters worse, all she could see was the Welcome Screen...it seems everything was gone in the original one LINE. Not to mention the second one LINE.

She's scared and asks me to check whether contacts and chat history exist or not. I want she calm down and relogin in. Fortunately everything is fine. Now she turns tears into smiles.

But where is the second one LINE? Ellen's about to pass out...I said to her don't panic and I reactivate LINE in "Dual Messenger". Guess what? The second one LINE shows up again.