Vertical artifacts after replacing display

I had a broken digitizer and tried to replace the screen (LCD+digitizer)

So cable connected and tested -> Working

Glue added, cable reconnected and slightly pressed on glue while trying to get that cable to bend the right way. When everything was in place, I tested the display again and found suddenly vertical lines extending from bright (e.g. white) elements shown over the whole height of the display.

This now happened twice to me and I can't figure out, what I may have done wrong.

Any ideas?

Start:

Kinda invisible:

After boot