Did you use hot water to make? I used room temperature water and don’t have this problem thou. You might wanna try using room temp water? :)
I use lukewarm or room temperature water with a shaker. Turns out nice and creamy cos of the shaker. No issues too.
What brand is that? Never had an issue if I mix for a longer time with a spoon even with room temp
usually I use 40-50°C water to make the milk
You may wish to try Friso Mum Gold
Use 40degree temp