Strange Behavior of Incognito windows

Whenever I open an incognito window on my Windows 10 (with Bitdefender installed) PC using Chrome or Firefox and search something on Google, the browsers initially display the results on a white page. However, after refreshing the page once or twice, it changes to the normal black display. What could be the reason for this, and how can I fix it?

white.PNG black.PNG

However Brave browser does not contain this prb. Anybody ?

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