Yes it’s common, I have a couple of friends with older baby’s and I remember their hair looking ridiculous around this age where they had gone bald in patches 😂
Baby hair is very very fragile so it’s normal to fall out, mine has a bald patch on the back of her head from how she sleeps which is turning her head left to right every 10 mins 🤣
I think it's pretty common. My 6 month old daughter has a thin patch of hair on the back of her head from when she's rolling round playing or moving in her sleep 😂 I'm sure now she's sitting up to play, it'll grow again