As an Android developer, the only thing I can be sure of is that configuration changes force the activity to be restarted. This includes screen orientation (portrait, landscape), so Chrome has to be destroyed and recreated, returning a blank/stale landscape content instead.
From Android Developers - Handle configuration changes
Handle configuration changes
Some device configurations can change during runtime (such as screen orientation, keyboard availability, and when the user enables multi-window mode). When such a change occurs, Android restarts the running
onDestroy() is called, followed by
onCreate()). The restart behavior is designed to help your application adapt to new configurations by automatically reloading your application with alternative resources that match the new device configuration.
To properly handle a restart, it is important that your activity restores its previous state. [...]
(Also, list of configuration changes)
I cannot reproduce this issue on my device*, but from the screenshots, the recent list is always shown in portrait mode, so there is a change from landscape to portrait between triggering the "recent apps list" event and showing it. I'm not sure about the order of the events for screen rotated, app destroyed, and app recreated, but most possibly it is destroyed-rotated-recreated, thus the app is not ready yet to re-render the activity (since an activity also cannot run while on the background), returning a blank white screen or use its previous state (the stale landscape content) instead.
The "fix" ― if it is possible ― is to allow showing "recent apps list" in landscape mode.
*The reason I cannot reproduce this issue is that my device allows showing "recent apps list" in landscape mode, so the thumbnail is shown correctly. However, when I rotate to portrait while on the list, the thumbnail will be shown squished as the screenshot.
Also, the restart may be observed more easily by rotating the screen while Chrome is active: after the rotation, Chrome will re-render the content to current available space.
Lastly, I do not know why the recent apps list is forced on portrait mode, but that is out of the question's scope.