Hello
Today I saw that during my workout the MPA screen in the EBC app stays on the same level. After finishing my workout there was no MPA activity only a straight purple line. Is there an issue with the Android EBC app.
The Endurance Builder workout touches TP but doesn’t exceed it.
Had you ridden in Slope mode and spent enough time above TP you would see some minor MPA dips.
The thumbnail chart for each workout shows whether MPA drawdown is expected along with predicted difficulty (shaded graph).
Compare that to this Hardness Test workout. 
Reference (detailed article) –
MPA™ – Maximal Power Available – Xert (baronbiosys.com)
The workout ride has been performed in erg mode and not in slope mode. But a straight MPA line with no little curve in it looks for me very strange. The whole ride my MPA field give me 1030 as number
Correct. AUTO is ERG mode (trainer control) in Xert EBC. The trainer controls resistance to match target watts. In this case you never exceed 100% TP to trigger any MPA drawdown. With no drawdown MPA remains equal to your PP.
Here’s a better example.
If I open the Endurance Builder workout in Workout Designer and change the 3 minutes at 100% TP to 110% and click Refresh, the chart changes to this.
If I edit further and change the ramps to/from 110%, the result looks like this.
I.e., a more pronounced MPA drawdown since more time is spent above TP (yellow into orange zone).
Had you ridden the original workout in Slope/Resistance mode and used gears/cadence to attain targets, the possibility of MPA drawdown exists as you may overshoot 100% TP during those intervals.
MPA will never curve downward unless some portion of a workout or ride includes sufficient time above TP at a given watts. Even a workout sprinkled with 10 second red spikes followed by low watt long recoveries can show a flatline MPA because the red spikes were not high enough in watts or long enough in seconds to trigger MPA drawdown.
Watch this section of the D2 Academy series video –
Episode D2 - Mastering Xert - Discover - MPA - YouTube
Thx. That is a nice explanation how it works. Thx all for the great support on this forum. 