I couldn't find anything like this in the bugs already.
So I was mining a hole in the ground for a slime farm on a realm. When I mined a stone block (stone, diorite, etc.) it flashed white for a fraction of a second. I have an efficiency IV, Unbreaking II, Silk touch diamond pickaxe.  This doesn't happen every time but feels like around 25% of the time. I didn't do anything special to trigger it.

I don't have a direct video, but a link to a youtube video I took to show this bug.
https://www.youtube.com/watch?v=F3-LW7hiwgE