Have had the machine for about 9 months. I'm beginning to notice some issues with the second shot. Here is the sequence

1) froth milk
2) pull shot. so far so good
3) clean porta filter (1 gap?)
4) froth milk (1-2 min?)
5) pull shot: machine clogs up with same amount of coffee and grind setting.

This sequence is very reproducible

Is the group head cooling that much between the shots?

CR

I'm pretty new to the game of prosumer espresso, and have only had my MaraX for ~2 months, but from what I read the order should be almost opposite if you want most consistent temperature and most steam power (while in "X Mode", of course).

My process is:

1. Pull shot
2. Clean portafilter, group, while pressure builds to ~1.5 bar
3. Steam milk
... reapeat

I've never had any issues with this, although pressure/temperature will start to struggle the more it's repeated.
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I don't think the machine cooling could affect the flow that much - What grinder are you using , and are you purging before making the first shot ?. Most grinders will have certain amount of stale coffee in the burr chamber that will affect the first shot if you don't purge that coffee out . Then the second coffee will be much fresher grind, and pour differently .
Try an experiment - purge 7-10 grams before making any coffee, then make your two coffees and see if they still differ. I know it seems wasteful, but it's why single dosing grinders and zero retention grinders are becoming more popular for home users

Mazzer mini with doser less mod. little to no coffee in grinder in between grinds. Have "flushing" system for the grinder.

Will give your suggestion a shot!