Blocks acting like they're being mined on their own but don't break

I play in bedrock for windows 10 and I was in my boyfriends world, I was building a dock and I set down an oak log and noticed it had a black dot in the middle as if it was being mined, so I went to take a picture of it to show my boyfriend but then realized it was acting as if it was being mined, but very slowly and when it looked like it was about to break, the mining animation just went away. I took a couple videos of it but had to stop and let the first video save as I took it on snapchat, so it ended up "mining" itself very slowly for about 3 minutes.