App Version: 70.0.3538.17
iOS Version: iOS12
Device: iPhone XS Max, iPhone8
URL: incognito tab switcher

Steps to reproduce:
  1. Open app and go into the tab switcher
  2. Switch to incognito tabs
  3. Open a tab via the + button
  4. Press the tab switcher icon
  5. Open another tab via the + button (watch the bottom of the screen)

Observed results:
White line is briefly shown above the footer bar

Expected results:
No white line should be visible.

Number of times you were able to reproduce: 5/5
Bug reproducible after clean install: Yes
Bug reproducible after clearing cache and cookies: Yes
Observed behavior in Chrome Mobile on Android: n/a
Check for similar behavior on Firefox/Safari: n/a
Bug reproducible on current stable build (App Version, iOS Version): No on M69
Bug reproducible on the current beta channel (dogfoody) build (App Version, iOS Version): Yes on M70 and M71

Video: https://drive.google.com/file/d/1TUvIEL4BIODC180aRB33hU9bA2jEXXpZ/view?usp=sharing