App Version: 70.0.3538.48 Beta
iOS Version: 10.3.3, 11.4.1, 12.0, 12.1 beta 2
Device: iPhone only

Steps to reproduce:
1. Launch chrome 
2. Go to nytimes.com
3. Scroll the page to fullscreen
4. Scroll up the page while page scrolling
4. Tap on back button
5. Tap on forward button
6. Scroll the page down

Observed results:
Notice that webview doesn’t go to fullscreen

Note 1: Able to reproduce in M71 even on enabling BrowserContainer or Private Fullscreen API flags
Note 2: After step 6 slightly scroll up and start scroll down then the page will go to fullscreen

Expected results:
Webview should go to fullscreen

Number of times you were able to reproduce: 5/5
Bug reproducible after clean install: Yes
Bug reproducible after clearing cache and cookies: Yes
Bug reproducible on Chrome Mobile on Android: Not tested
Bug reproducible on Safari/Firefox: Firefox: No, Safari: No
Bug reproducible on current stable build (App Version, iOS Version): Yes on M69 
Bug reproducible on the current beta channel build (App Version, iOS Version): No on M70

Link to video:
https://drive.google.com/file/d/1ZuKyj8hPG5_1dqx9qnCU8e86zLhlISlm/view?usp=sharing