Some users may notice that, while using Chrome, the Messenger chat window will flash open and closed. While it might immediately appear to be a bug, there’s nothing wrong with the chat or your website. This is actually a performance feature in Chrome that doesn’t work well with the Messenger chat feature.
To disable this feature on your browser, follow these steps:
How to disable “Use hardware acceleration when available” for Chrome
Access your Browser settings (Chrome)
Click on System on the left hand corner list
Toggle off Use hardware acceleration when available.