The line changes its angle automatically when moved vertically.

Hello Resulticks Edge Solution Technologies Private Ltd,

Sorry to hear that you ran into this snag. I tried following the same steps in the video but was unable to replicate the behavior after aligning the lines. Here's a quick recording of my attempt:

Since the behavior appears to be isolated to your installation, try doing a repair of Storyline 360 to see if this helps. If the issue persists, open a case with our support team here so we can have our support engineers take a closer look at the behavior.