Happens to me to on Windows 7 as well. Version 0.61.52 Chromium: 73.0.3683.86 (Official Build) (64-bit)
However, what I notice is that it doesn’t exactly delete, rather it selects the text written during the first few milliseconds and then as I continue typing, overwrites it.
Also, I’ve noticed sometimes it doesn’t happen immediately upon starting up Brave, only after awhile of use (not sure how long exactly), sometimes it doesn’t happen at all.
Also, I’m guessing it might be related to the new tab page loading. The new tab page doesn’t load instantaneously for me, it lags a few milliseconds (I approximate) before the wallpaper and stats show up, and as they show up, the overwrite happens.
I wanted to add a gif, but right now it’s not happening so I can’t record it. I’ll add a gif if/when it starts happening again.