Could be your espresso is still degassing.. So a swirl and tap with your espresso just like your frothed milk, before pouring the milk in.

Tap your milk after you froth, and before you pour into the espresso. While frothing bigger bubbles get trapped under small fine bubbles on top, hence appearing after it sits and the big bubble pushes its way up.

Hye, what milk brand are you using ? I used to have that problem with certain milk brand such as the dutch lady ones.  For me, Farm fresh seems to do a great job and it's smooth without the bubbles. It holds well. Different milk brands seems to give different results.

Try Hot shots at publika, I think they do delivery too.