U2515H, Vertical lines

Hi there,

 First and foremost let me describe what I have.

Triple monitor setup: Two U2515H (both running on brand new HDMI cables) and one U2312HM (running on a brand new DVI cable)
GPU: GTX 1080 with latest drivers already installed
OS: Windows 10 Pro, software fully updated
Issue: Vertical lines on replacement U2515H monitor

There was a dead pixel on the U2515H and received a replacement unit around two weeks back. The replaced monitor worked flawlessly until today, where vertical lines appeared on the entire screen in a uniform regular pattern. I am seeing a variety of colors from white lines to pinkish to greenish on a white background. I've done the following troubleshooting but to no avail, so I would like to see if anyone can help me out. Meanwhile I will also be contacting my local dell support, but unfortunately they're already closed for the day. So I would like to log this down on the forum as well for other users! 

Troubleshooting 1: Followed the instructions on page 55 of the U2515H support manual and did a Self-Test and reseted to factory settings.
Results: Everything was working normally as expected in the manual 

Troubleshooting 2: Page 56 on the Built-in Diagnostics.
Results: All the screens (Gray, red, green, blue, black, white, text screen) were normal. I cant visually see any lines. 

Troubleshooting 3: Page 58 on Horizontal/Vertical line issues
Results: Self-test mode worked; no bent or broken pins on HDMI cable and input source (I compared with my other working U2515H); same normal results for built-in diagnostics 

Troubleshooting 4: Changed to other HDMI port and repeated the above 3 troubleshooting.
Results: Same issues and results persisted 

Troubleshooting 5: Swapped HDMI cable and power cable with the other U2515H and tested on both HDMI ports
Results: Same issues and results persisted 

Troubleshooting 6: Swapped HDMI slots on GPU and re-inserted GPU to ensure that it has a tight fit
Results: Same issues and results persisted 

Troubleshooting 7: Run on another windows laptop and MacBook Pro using the U2515H as an external monitor
Results: Same issues and results persisted

Troubleshooting 8: Disconnected other monitors to make it a single monitor set up and continued swapping HDMI cables and power cables
Results: Same issues and results persisted 

Troubleshooting 9: This time round I left the HDMI cable plugged in and ran a built-in diagnostic
Results: A few lines appeared uniformly on the gray screen, but for the other red/green/blue/black/white/text they are all normal with no visible lines. 

Hence with the above troubleshooting, I cant conclude if it is a monitor issue (cause built-in diagnostics doesn't show any lines), or a desktop/GPU issue (cause my other monitors aren't affected with any of the combinations or cables or testing, and also tested with other laptops). 

Can someone further advise on what other methods should I try out? If I've received a possible defective replacement set, can it be replaced again or something? (Cause this isn't a dead pixel issue)

 Can someone advise me on how can I upload images? I clicked on "insert/edit" image, but there are no options to upload them