Sticky poo help

I’ve noticed that when baby wakes up in the middle of night for a feed - he has really really sticky poo, to the point I have to carefully peal his nappy off as it’s joint to his skin. It’s a little bit and it’s happened for past 2/3 nights.

During the day poo is normal, it’s only sticky after his long stretch of sleep overnight.

Baby is exclusively breastfed and there has been no change in my diet. Baby is 12 weeks.

Anyone know what this could be? If it’s cause for concern?