Hello there! TheLoneWanderer,
Thanks for letting us know your experience with your beloved Samsung Galaxy A71 having issues with the vertical white and green lines on screen. I feel that you've cared for your device so much, that if something amiss, you will be easily aware of it and got you worried. If my device is facing similar experience, I will be bothered too. But don't fret, I will try to assist you to the best of my abilities.
Before you try out the below recommendations as to your solution, be sure to check if your device's software are updated with the latest version. Please check how to update your mobile device's software in the following order.
Step 1. Go to Settings > Software update.
Step 2. Tap on Download and install.
Step 3. Follow the on-screen instructions.
Step 4. Restart you device.
If that doesn't solve the issue, you may submit an error report through the Samsung Members app as follows:
Step 1. Launch the Samsung Members app, and then tap the Support icon for more options.
Step 2. Scroll and select Error reports.
Step 3. Choose a category of your concern. Select "Display".
Step 4. Choose the frequency of the issue you are experiencing. Enter issue details or attach a video or screenshot. Then press Send icons to complete the report.
And if the issue remains, you may bring your device to the nearest Samsung Authorized Service Center in your area. Rest assured that your device will undergo an assessment to pinpoint the root cause of the issue(s). Our team of Samsung engineers and technicians will guide you and offer solutions to restore it.
or book an appointment with the Samsung Members app as follows:
Support > Book an appointment to set one.
Should you need further assistance and guidance, you may contact us via our Samsung Customer Care support channels below.
I also have this problem just today, in fact this very evening. It started as faint black line in the middle and few more seconds it became discolored and then turned white. And I already had downloaded the latest software last week. This A71 has been with me for almost 3 years and never dropped it nor putting the phone in tight spaces, same issues as the other A71 users even with utmost care for reasons that to avoid buying new decent phones nowadays because they are expensive.